Precision-folded, high strength, fatigue-resistant structures and sheet therefor

ABSTRACT

Precision-folded, high strength, fatigue-resistant structures and a sheet therefore are disclosed. To form the structures, methods for precision bending of a sheet of material along a bend line and a sheet of material formed with bending strap-defining structures, such as slits or grooves, are disclosed. Methods include steps of designing and then separately forming longitudinally extending slits or grooves through the sheet of material in axially spaced relation to produce precise bending of the sheet when bent along the bend line. The bending straps have a configuration and orientation which increases their strength and fatigue resistance, and most preferably slits or arcs are used which causes edges to be engaged and supported on faces of the sheet material on opposite sides of the slits or arcs. The edge-to-face contact produces bending along a virtual fulcrum position in superimposed relation to the bend line. Several slit embodiments suitable for producing edge-to-face engagement support and precise bending are disclosed. With these teachings, forming numerous three-dimensional load-bearing structures from a two dimensional sheet are enabled. Examples of straight and curved beams, chassis, and exoskeletons are disclosed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.12/468,654 filed May 19, 2009, now abandoned, which is a Continuation ofU.S. patent application Ser. No. 11/384,216 filed Mar. 16, 2006, nowU.S. Pat. No. 7,534,501, which claims the benefit of U.S. ProvisionalApplication No. 60/663,392 filed Mar. 17, 2005, and the '216 applicationis a Continuation-in-Part of U.S. patent application Ser. No. 10/672,766filed Sep. 26, 2003 and now U.S. Pat. No. 7,152,449 B2, which is aContinuation-in-Part of U.S. patent application Ser. No. 10/256,870filed Sep. 26, 2002 and now U.S. Pat. No. 6,877,349 B2. All of the aboveapplications are incorporated herein by reference for all purposes intheir entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates, in general, to the designing andprecision folding of sheets of material and the manufacture ofstructures therefrom. More particularly, the present invention relatesto processes of designing, preparing and manufacturing, including, butnot limited to, ways of preparing sheet material, in order to enableprecision folding and to the use of such processes for rapidtwo-dimension-to-three-dimensional folding of high strength,fatigue-resistant structures or assemblies.

2. Description of Related Art

A commonly encountered problem in connection with bending sheet materialis that the locations of the bends are difficult to control because ofbending tolerance variations and the accumulation of tolerance errors.For example, in the formation of the housings for electronic equipment,sheet metal is bent along a first bend line within certain tolerances.The second bend, however, often is positioned based upon the first bend,and accordingly, the tolerance errors can accumulate. Since there can bethree or more bends which are involved to create the chassis orenclosure for the electronic components, the effect of cumulativetolerance errors in bending can be significant. Moreover, the tolerancesthat are achievable will vary widely depending on the bending equipment,and its tooling, as well as the skill of the operator.

One approach to this problem has been to try to control the location ofbends in sheet material through the use of slitting or grooving. Slitsand grooves can be formed in sheet stock very precisely, for example, bythe use of computer numerically controlled (CNC) devices which control aslit or groove forming apparatus, such as a laser, water jet, punchpress, knife or other tool.

Referring to FIG. 1, a sheet of material 21 is shown which has aplurality of slits or grooves 23 aligned in end-to-end, spaced apartrelation along a proposed bend line 25. Between pairs of longitudinallyadjacent slits or grooves are bending webs, splines or straps 27 whichwill be plastically deformed upon bending of sheet 21. Webs 27 hold thesheet together as a single member. When grooves that do not penetratethrough sheet 21 are employed, the sheet of material is also heldtogether by the web of material behind each groove.

The location of grooves or slits 23 in sheet 21 can be preciselycontrolled so as to position the grooves or slits on bend line 25 withinrelatively close tolerances. Accordingly, when sheet 21 is bent afterthe grooving or slitting process, the bend occurs at a position that isvery close to bend line 25. Since slits can be laid out on a flat sheetof material precisely, the cumulative error is much less in such abending process, as compared to one in which bends are formed by a pressbrake, with each subsequent bend being positioned by reference to thepreceding bend.

Nevertheless, even a grooving-based or slitting-based bending of sheetmaterial has its problems. First, the stresses in bending webs or straps27, as a result of plastic deformation of the webs and slitting at bothends of webs 27, are substantial and concentrated. For grooving, thestresses on the material behind or on the back side of the groove alsoare substantial and very concentrated. Thus, failures at webs 27 and/orbehind grooves 23 can occur. Moreover, the grooves or slits do notnecessarily produce bending of webs 27 directly along bend line 25, andthe grooving process is slow and inconsistent, particularly when millingor point cutting V-shaped grooves. Grooving, therefore, is not inwidespread commercial use.

As can be seen in FIGS. 1A and 1B, if sheet 21 is slit, as is shown at23 a and/or grooved, as shown at 23 b, and then bent, bending webs 27 aand 27 b will experience plastic deformation and residual stress. Forslit 23 a, of course, material will be completely removed or severedalong the length of the slit. For V-shaped groove 23 b, there will be athin web 29 between groove 23 b and the convex outside of the bend, butit also will be plastically deformed and highly stressed. The bend forV-shaped grooving will normally be in a direction closing groove 23 b sothat the side faces come together, as shown in FIG. 1B. Loading of thebent structure of FIGS. 1A and 1B with a vertical force F_(V) and/or ahorizontal force F_(H) will place the bend, with the weakening slitsand/or grooves and the plastically deformed straps or webs 27 a, 27 b,as well as thin web 29, under considerable stress. Failure of thestructure will occur at lower force levels than if a non-slitting ornon-grooving bending process was used.

Another scheme for sheet slitting to facilitate bending has beenemployed in the prior art. The slitting technique employed to producebends, however, was designed primarily to produce visual or decorativeeffects for a sculptural application. The visual result has beendescribed as “stitching,” and the bends themselves have beenstructurally reinforced by beams. This stitched sculpture was exhibitedat the New York Museum of Modern Art by at least 1998, and the sheetslitting technique is described in Published United States PatentApplication U.S. 2002/0184936 A1, published on Dec. 12, 2002, (the“Gitlin, et al Application.”). The sculpture is also shown and describedin the publication entitled “Office dA” by Contemporary WorldArchitects, pp. 15, 20-35, 2000. FIGS. 2, 2A and 2B of the presentdrawing show one example of the stitching technique employed.

One embodiment of the Office dA or Gitlin, et al. Application is shownin FIG. 2. A plurality of slits 31 is formed in a sheet material 32.Slits 31 are linear and offset laterally of each other along oppositesides of a bend line 33. The slits can be seen to longitudinally overlapso as to define what will become bending splines, webs, straps or“stitches” 34 between the overlapped slit ends. FIGS. 2A and 2B show anenlarged side elevation view of one end of one slit in sheet 32, whichhas been bent along bend line 33 by 90 degrees, and sheet portions 35and 36 on opposite sides of the bend line are interconnected by thetwisted straps or “stitches” 34, which twist or stitch between the 90degree sheet portions 35,36. The architects of the New York Museum ofModern Art sculpture recognized that the resulting bend is notstructurally very strong, and they have incorporated partially hiddenbeams welded into the sculpture in the inner vertices of each of thestitched bends.

Since slits 31 are parallel to bend line 33, straps 34, which also havea constant or uniform width dimension, are twisted or plasticallydeformed in torsion over their length, with the result that at the endof a 90° bend a back side of the strap engages face 38 on the other sideof slit 31 at position 37. Such engagement lifts sheet portion 35 upaway from face 38 on sheet portion 36, as well as trying to open end 40of the slit and producing further stress at the slit end. The result ofthe twisting of straps 34 and the lifting at the end of the bend is agap, G, over the length of slit 31 between sheet portion 35 and face 38.Twisted straps or stitches 34 force sheet portion 35 off of face 38 andstress both slit ends 40 (only one slit end 40 is shown but the samestress would occur at the other slit end 40 of the slip 31 shown inFIGS. 2A and 2B).

Gaps G are produced at each slit 31 along the length of bend line 33 onalternative sides of the bend line. Thus, at each slit a sheet portionis forced away from contact with a slit-defining face instead of beingpulled into contact with, and thus full support by, the face.

Moreover, and very importantly, the slitting configuration of FIG. 2stresses each of straps 34 to a very high degree. As the strap length isincreased (the length of overlap between the ends of slits 31) toattempt to reduce the stress from twisting along the strap length, theforce trying to resiliently pull or clamp a sheet portion against anopposing face reduces. Conversely, as strap length 34 is decreased,twisting forms micro tears in the constant width straps with resultantstress risers, and the general condition of the twisted straps is thatthey are overstressed. This tends to compromise the strength of the bendand leaves a non-load bearing bend.

A vertical force (Fv in FIG. 2B) applied to sheet portion 35 willimmediately load twisted and stressed strap 34, and because there is agap G the strap will plastically deform further under loading and canfail or tear before the sheet portion 35 is displaced down to engagementwith and support on face 38. A horizontal force F_(H) similarly willtend to crush the longitudinally adjacent strap 34 (and shear strap 34in FIG. 2B) before gap G is closed and the sheet portion 35 is supportedon the opposing slit face 38.

Another problem inherent in the slitting scheme of FIGS. 2-2B and theGitlin, et al. Application is that the constant strap width cannot bevaried independently of the distance between slits, and the strap widthcannot be less than the material thickness without stressing the strapsto the extreme. When slits 31 are parallel to each other andlongitudinally overlapping, the strap width, by definition, must equalthe spacing or jog between slits. This limits the flexibility indesigning the bends for structural loading of the straps. Still further,the slits terminate with every other slit end being aligned and directedtoward the other. There is no attempt, therefore, to reduce stressrisers and micro-crack propagation from occurring at the ends of theslits, and aligned slit ends can crack under loading.

The sheet slitting configuration of FIGS. 2-2B, therefore, can bereadily employed for decorative bends, but it is not optimally suitedfor bends which must provide significant structural support and fatigueresistance.

The Gitlin et al. Application also teaches the formation of curved slits(in FIGS. 10 a, 10 b), but the slits again parallel a curved bend lineso that the width of the bending straps is constant, the straps extendalong and parallel to the bend line, not across it, the straps aretwisted in the extreme, the slit ends tend to direct micro-cracks andstress concentrations to the next slit, and the application teachesemploying a slit kerf which results in engagement of the opposite sideof the slit, at 37, only at the end of the bend.

A simple linear perforation technique also was used by the samearchitects in an installation of bent metal ceiling panels in a pizzarestaurant in Boston. Again, the bent sheet components by linearperforation were not designed to bear significant unsupported loadsalong the bends.

Slits, grooves, perforations, dimples and score lines also have beenused in various patented systems as a basis for bending sheet material.U.S. Pat. No. 5,225,799 to West et al., for example, uses agrooving-based technique to fold up a sheet of material to form amicrowave wave guide or filter. In U.S. Pat. No. 4,628,161 to St. Louis,score lines and dimples are used to fold metal sheets. In U.S. Pat. No.6,210,037 to Brandon, slots and perforations are used to bend plastics.The bending of corrugated cardboard using slits or die cuts is shown inU.S. Pat. No. 6,132,349 and PCT Publication WO 97/24221 to Yokoyama, andU.S. Pat. Nos. 3,756,499 to Grebel et al. and 3,258,380 to Fischer, etal. Bending of paperboard sheets also has been facilitated by slitting,as is shown in U.S. Pat. Nos. 5,692,672 to Hunt, 3,963,170 to Wood and975,121 to Carter. Published U.S. Patent Application No. US 2001/0010167A1 also discloses a metal bending technique involving openings, notchesand the like and the use of great force to produce controlled plasticflow and reduced cracking and wrinkling.

In most of these prior art bending systems, however, the bend formingtechnique greatly weakens the resulting structure, or precision bendsare not capable of being formed, or bending occurs by crushing thematerial on one side of the bend. Moreover, when slitting is used inthese prior art systems, in addition to structural weakening and thepromotion of future points of structural failure, the slitting can makethe process of sealing a bent structure expensive and difficult. Theseprior art methods, therefore, are less suitable for fabricatingstructures that are capable of containing a fluid or flowable material.

The problems of precision bending and retention of strength are muchmore substantial when bending metal sheets, and particularly sheets ofsubstantial thickness. In many applications it is highly desirable to beable to bend metal sheets with low force, for example, by hand with onlyhand tools, or with only moderately powered tools. Such bending of thickmetal sheets, of course, poses greater problems.

In another aspect of the present invention the ability to overcome priorart deficiencies in slitting-based bending of sheet material is appliedto eliminate deficiencies in prior art metal fabrication techniques andthe structures resulting therefrom.

A well known prior art technique for producing rigid three-dimensionalstructures is the process of cutting and joining together parts fromsheet and non-sheet material. Jigging and welding, clamping and adhesivebonding, or machining and using fasteners to join together severaldiscrete parts has previously been extensively used to fabricate rigidthree-dimensional structures. In the case of welding, for example, aproblem arises in the accurate cutting and jigging of the individualpieces; the labor and machinery required to manipulate a large number ofparts, as well as the quality control and certification of multipleparts. Additionally, welding has the inherent problem of dimensionalshape warping caused by the heat-affected zone of the weld.

Traditional welding of metals with significant material thickness isusually achieved by using parts having beveled edges often made bygrinding or single point tools, which add significantly to thefabrication time and cost. Moreover, the fatigue failure ofheat-affected metals is unpredictable for joints whose load-bearinggeometries rely entirely on welded, brazed or soldered materials.Fatigue failure of welds usually is compensated for by increasing themass of the components, which are welded together and the number anddepth of the welds. The attendant disadvantage of such over design is,of course, excessive weight.

With respect to adhesively bonding sheet and non-sheet material alongthe edges and faces of discrete components, a problem arises from thehandling and accurate positioning the several parts and holding orclamping them in place until the bonding method is complete.

Another class of prior art techniques related to the fabrication ofthree-dimensional structures are the Rapid Prototyping methods. Theseinclude stereo lithography and a host of other processes in which adesign is produced using a CAD system and the data representation of thestructure is used to drive equipment in the addition or subtraction ofmaterial until the structure is complete. Prior art Rapid Prototypingtechniques are usually either additive or subtractive.

The problems associated with subtractive Rapid Prototyping methods arethat they are wasteful of materials in that a block of material capableof containing the entire part is used and then a relatively expensivehigh-speed machining center is required to accurately mill and cut thepart by removal of the unwanted material.

Problems also exist with prior art additive Rapid Prototypingtechniques. Specifically, most such techniques are optimized for a verynarrow range of materials. Additionally, most require a specializedfabrication device that dispenses material in correspondence with thedata representing the part. The additive Rapid Prototyping processes areslow, very limited in the scale of the part envelope and usually do notmake use of structurally robust materials.

Generally in the prior art, therefore, sheet slitting or grooving toenable sheet bending has produced bends, which lack the precision andstrength necessary for commercial structural applications. Thus, suchprior art sheet bending techniques have been largely relegated to lightgauge metal bending or decorative applications, such as sculpture.

In a broad aspect of the present invention, therefore, it is animportant object of the present invention to be able to bend sheetmaterial in a very precise manner and yet produce a bend, which iscapable of supporting substantial loading and is resistant to fatiguefailures.

Another object of this aspect of the present invention is to provide amethod for precision bending of sheets of material using improvedslitting techniques, which enhance the precision of the location of thebends, the strength of the resulting structures and reducestress-induced failures.

Another object of the present invention is to provide a precision sheetbending process and a sheet of material which has been slit or groovedfor bending and which can be used to accommodate bending of sheets ofvarious thicknesses and of various types of non-crushable materials.

Another object of the present invention is to provide a method forslitting sheets for subsequent bending that can be accomplished usingonly hand tools or power tools which facilitate bending but do notattempt to control the location of the bend.

Another object of the present invention is to be able to bend sheetmaterial into high strength, three-dimensional structures having precisedimension tolerances.

It is another object of the present invention to be able to bend sheetmaterials into precise three-dimensional structures that are easily andinexpensively sealed thus enabling the containment of fluid or flowablematerials.

In a broad aspect of the present invention relating to the use ofslit-based bending to enhance fabrication and assembly techniques, it isan object of the present invention to provide a new Rapid Prototypingand Advanced Rapid Manufacturing technique that employs a wide range ofmaterials including many that are structurally robust, does not employspecialized equipment other than what would be found in any modernfabrication facility, and can be scaled up or down to the limits of thecutting process used.

It is another object of this aspect of the present invention to providefeatures within the sheet of material to be bent that assist in theaccurate additive alignment of components prior to and after the sheetmaterial is bent.

A further object of the present invention is to provide a fabricationmethod that serves as a near-net-shape structural scaffold for multiplecomponents arranged in 3D space in the correct relationship to eachother as defined by the original CAD design process.

It is a further object of the present invention to provide a method offabricating welded structures that employs a smaller number of separateparts and whose edges are self jigging along the length of the bends andwhose non-bent edges provide features that facilitate jigging andclamping in preparation for welding. In this context it is yet anotherobject of the present invention to provide a superior method of jiggingsheet materials for welding that dramatically reduces warping anddimensional inaccuracy caused by the welding process.

Yet another object of the present invention is to provide a novel weldedjoint that provides substantial load-bearing properties that do not relyon the heat affected zone in all degrees of freedom and thereby improveboth the loading strength and cyclical, fatigue strength of theresulting three-dimensional structure.

Still another object of the present invention is to provide a superiormethod for:

1) reducing the number of discrete parts required to fabricate a strong,rigid, dimensionally accurate three-dimensional structure, and

2) inherently providing a positioning and clamping method for thevarious sides of the desired three-dimensional structure that can beaccomplished through the bent and unbent edges of the present inventionresulting in a lower cost, higher yield fabrication method.

It is a further object of the present invention to provide a method offabricating a wide variety of fluid containing casting molds for metals,polymers, ceramics and composites in which the mold is formed from aslit, bent, sheet of material which can be either removed after thesolidification process or left in place as a structural or surfacecomponent of the finished object.

Still another object of the present invention is to provide a sheetbending method that is adaptable for use with existing slitting devices,enables sheet stock to be shipped in a flat or coiled condition andprecision bent at a remote location without the use of a press brake,and enhances the assembly or mounting of components within and on thesurfaces in the interior of enclosures formed by bending of the sheetstock after component affixation to the sheet stock.

Still another object of the present invention is to provide a precisionfolding technique that can be used to create accurate, precise,load-bearing folds in sheets of material, including but not limited to,metals, plastics, and composites.

Another object of the present invention is to provide a precisionfolding technique that allows folding around a virtual bend line andrequires considerably less force to accomplish the fold thanconventional bending techniques.

Another object of the present invention is to provide a precisionfolding technique that is essentially linearly scalable independently ofthe thickness or microstructural characteristics of the material

Another object of the present invention is to form the geometriesdescribed herein whether by a slitting/removal process, a severingprocess or by an additive process, and arrive at the advantages hereindescribed by any route.

Yet another object of the present invention is to provide a precisionfolding technique for folding a non-crushable material in which themicrostructure of the material remains substantially unchanged aroundthe fold.

The methods and discrete techniques for designing and precision foldingof sheet material, the fabrication techniques therefor, and thestructures formed from such precision bending of the present inventionhave other features and objects of advantage which will become apparentfrom, or are set forth in more detail in the following detaileddescription and accompanying drawings.

BRIEF SUMMARY OF THE INVENTION

In a broad aspect, a sheet of material for bending along a desiredbending line includes bending strap-defining structures formed in thesheet. The strap-defining structures are positioned to define at leastone bending strap in the sheet, the strap having a longitudinal strapaxis that is oriented and positioned to extend across the bend line.Moreover, the strap defining structures are configured and positioned toproduce bending of the sheet of material along the bend line.

In another aspect, a hollow beam includes two sheets of material. Thefirst sheet of material is formed for bending along a plurality of firstsheet bend lines by having a plurality of bending strap-definingstructures positioned proximate each of the bend lines, with the bendingstrap-defining structures configured to produce bending along the bendlines. A hollow beam is formed by securing the first sheet of material,being bent along first sheet bend lines, to a second sheet of material.

In yet another aspect, an exoskeletal framework includes a single sheetof material formed for bending along a plurality of bend lines. Thesheet of material is formed with a plurality of bending strap-definingstructures positioned proximate each of the bend lines, and the bendingstrap-defining structures are configured to produce bending. Bending thesheet of material along the bend lines results in a framework ofstructural members.

The precision-folded, high strength, fatigue-resistant structures andsheet therefor of the present invention has other features andadvantages which will be apparent from or are set forth in more detailin the accompanying drawings, which are incorporated in and form a partof this specification, and the following Detailed Description of theInvention, which together serve to explain the principles of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, top plan view of a sheet of material havingslits and grooves formed therein in accordance with one prior arttechnique.

FIG. 1A is an enlarged, fragmentary view, in cross section, takensubstantially along the plane of line 1A-1A in FIG. 1, of the sheet ofFIG. 1 when in a bent condition.

FIG. 1B is an enlarged, fragmentary view, in cross section, takensubstantially along the plane of line 1B-1B of FIG. 1, of the sheet ofFIG. 1 when in a bent condition.

FIG. 2 is a fragmentary, top plan view of a sheet of material having aplurality of slits formed therein using an alternative configurationknown in the prior art.

FIG. 2A is an enlarged fragmentary side elevation view of the sheet ofFIG. 2 bend by about 90 degrees.

FIG. 2B is a cross-sectional view taken substantially along the plane ofline 2B-2B in FIG. 2A.

FIG. 3 is a fragmentary, top plan view of a sheet of material slit inaccordance with one embodiment of the present invention.

FIGS. 4A-4D are fragmentary, top plan views of a sheet of material whichhas been slit according to the embodiment of FIG. 3 and which is in theprocess of being bent from a flat plane in FIG. 4A to a 90 degrees bendin FIG. 4D.

FIGS. 5A-5C′″ are fragmentary, cross-sectional views, takensubstantially along the planes of lines 5A-5A, in FIGS. 4A-4D duringbending of the sheet of material.

FIG. 6 is a top plan view of a sheet of material slit in accordance witha second embodiment of the present invention.

FIG. 7 is a top plan view of the sheet of FIG. 6 after being bent byabout 90 degrees.

FIG. 8 is an end view of the sheet of material of FIG. 7.

FIG. 8A is an enlarged, end elevation view, in cross section, of thesheet of material of FIG. 7 taken substantially along the plane of 8A-8Ain FIG. 7 and rotated by about 45 degrees from FIG. 8.

FIG. 8B is an enlarged, end elevation view, in cross section, of thesheet of material of FIG. 7 taken substantially along the plane of 8B-8Bin FIG. 7 and rotated by about 45 degrees from FIG. 8.

FIG. 9 is a fragmentary top plan view of a sheet of material slitaccording to a further alternative embodiment of the present invention.

FIG. 10 is a side elevation view of the sheet of FIG. 9 after bending byabout 90 degrees.

FIG. 10A is a fragmentary cross-sectional view taken substantially alongthe plane of line 10A-10A in FIG. 10.

FIG. 11 is a fragmentary, top plan view of a schematic representation ofa further alternative embodiment of a sheet of material havingstrap-defining structures constructed in accordance with the presentinvention.

FIG. 11A is a fragmentary top plan view of a slit of the configurationshown in FIG. 11 which has been formed using a rapid piercing lasercutting technique.

FIG. 12 is a fragmentary, top plan view of one sheet of material beforebending and assembly into a curved box beam.

FIG. 13 is a side elevation view of a curved box beam constructed fromtwo sheets of material each being slit as shown in FIG. 12.

FIG. 14 is an end elevation view of the beam of FIG. 13.

FIG. 15 is a top plan view of a sheet of material formed withstrap-defining structures and configured for enclosing a cylindricalmember.

FIG. 16 is a top perspective view of the sheet of material of FIG. 15 asbent along bend lines and mounted to enclose a cylindrical member.

FIG. 17 is a top perspective, exploded view of a corrugated assemblyformed using a sheet of material formed in accordance with the presentinvention.

FIG. 18 is a top perspective, exploded view of an alternative embodimentof a sheet of material formed in accordance with the present invention.

FIG. 19 is a top plan view of the slit sheet used to construct analternative embodiment of a corrugated deck prior to bending or folding.

FIG. 20 is a top perspective view of a corrugated sheet or deckconstructed using the slit sheet material of FIG. 19.

FIG. 21 is an enlarged, fragmentary perspective view substantiallybounded by line 21-21 in FIG. 20.

FIG. 21A is an enlarged, fragmentary, top plan view substantiallybounded by line 21A-21A in FIG. 19.

FIG. 22 is a schematic, end elevation view of a cylindrical memberconstructed using a corrugated sheet similar to that of FIGS. 19 and 20,scaled to define a cylindrical form.

FIG. 23 is an enlarged, fragmentary, side elevation view of a sheet ofmaterial slit in accordance with the present invention and having atongue or tab displaced to ensure predictable bending.

FIG. 23A is a reduced, end elevation view of the sheet of FIG. 23 duringbending.

FIG. 24 is a fragmentary, end elevation view of a sheet of material slitat an oblique angle to the plane of the sheet and shown during bending ato a complimentary angle.

FIG. 25 is a side elevation, schematic representation of a reel-to-reelsheet slitting line arranged in accordance with the present invention.

FIG. 26 is a top perspective view of a coiled sheet of material whichhas been slit, for example, using the apparatus of FIG. 25 and is in theprocess of being rolled out and bent into a three-dimensional structure.

FIGS. 27A-27G are top perspective views of a sheet of materialconstructed in accordance with the present invention as it is being bentinto a cross-braced box beam.

FIGS. 28A-28E are top perspective views of a sheet of materialconstructed in accordance with the present invention as it is being bentinto a chassis for support of components such as electrical components.

FIG. 29 is a top perspective, schematic representation of one embodimentof equipment suitable for low-force bending or folding of the slit sheetof the present invention.

FIG. 30 is a top perspective, schematic representation of anotherembodiment of sheet bending or folding process of the present invention.

FIG. 31 is a flow diagram of one aspect of the interactive design,fabrication and assembly processes for slit sheet material bending ofthe present invention.

FIGS. 32A-32E are top perspective views of a sheet of materialconstructed in accordance with the present invention as it is being bentinto a stud wall/ladder.

FIG. 33 is a top perspective view of a curved corrugated deck or panelconstructed in accordance with the present invention.

FIGS. 34A-34E are top perspective views of a sheet of material includingswing-out bracing and shown as it is being bent into a swing-out bracedbox-beam.

FIG. 35 is a top plan view of a sheet of material slit in accordancewith the present invention and including a single slit embodiment

FIG. 36 is a top perspective view of the sheet of FIG. 35 as bent into aroller housing.

FIG. 37 is a fragmentary top plan view of a sheet of material havingdiffering bend line termination slit configurations.

FIG. 38A is a top perspective view of a sheet of material constructed inaccordance with the present invention before being bent into a chassis.

FIG. 38B is a schematic, top perspective view of a sheet of material asin FIG. 38A after being bent into a chassis.

FIG. 38C is a top perspective view of several sheets of material as inFIG. 38A after being bent into a transitionary form of a chassis andstacked.

FIG. 39A is a top view of two sheets of material constructed inaccordance with the present invention before being formed and joinedinto a curved beam.

FIG. 39B is a top perspective view of a curved channel constructed inaccordance with the present invention from a sheet similar to that shownin FIG. 39A.

FIG. 39C is a top perspective view of a closed, hollow curved beamconstructed in accordance with the present invention from two sheetssimilar to those shown in FIG. 39A.

FIGS. 40A-H are perspective views of a sheet of material constructed inaccordance with the present invention before and in phases of beingfolded into a skeletal structure.

FIG. 41 is a perspective view of a corner portion of a skeletalstructure according to the present invention before and in phases ofbeing folded.

FIG. 42A is a perspective view of a corner portion as shown in FIG. 41.

FIG. 42B is a side view of an edge slot as shown in FIG. 42A

FIG. 42C is a side view of an alternate embodiment of an edge slot.

FIG. 43A is a top view of a sheet of material constructed in accordancewith the present invention before being formed into a curved exoskeletalstructure.

FIG. 43B is a perspective view of a sheet of material as shown in FIG.43A after being formed into a curved exoskeletal structure.

FIG. 43C is a top view of a portion of a sheet of material similar tothat shown in FIG. 43A before being formed into a curved exoskeletalstructure.

FIG. 44 is a perspective view of another sheet of material formed into athree dimensional structure in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to those embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims.

The present method and apparatus for precision bending of sheet materialis based upon the slitting geometries disclosed in prior applications,U.S. patent application Ser. No. 09/640,267, filed Aug. 17, 2000, nowU.S. Pat. No. 6,481,259 B1, and entitled METHOD FOR PRECISION BENDING OFA SHEET OF MATERIAL AND SLIT SHEET THEREFOR, and U.S. patent applicationSer. No. 10/256,870, filed Sep. 26, 2002 and entitled METHOD FORPRECISION BENDING OF SHEET OF MATERIALS, SLIT SHEETS AND FABRICATIONPROCESS, now U.S. Pat. No. 6,877,349 B2, which are incorporated hereinby reference in their entirety.

One embodiment of the precision and high strength bending process andapparatus of the present invention can be described by reference toFIGS. 3-5. In FIG. 3 a sheet of material 41 is formed with a pluralityof bending strap-defining structures, in this case slits, generallydesignated 43, along a bend line 45. Slits 43, therefore, arelongitudinally extending and in end-to-end spaced relation so as todefine bending webs or straps 47 between pairs of slits 43. In FIG. 3,slits 43 are provided with stress reducing structures at ends thereof,namely openings 49, so as to effect a reduction in the stressconcentration in bending webs 47. It will be understood from thedescription below, however, that stress reducing structures, such asenlarged openings 49 in FIG. 3, are not required for realization of thebenefits of the precision bending system of the present invention.

For the embodiment of slits 43 shown in FIG. 3, however, eachlongitudinally extending slit between the slit ends is laterally ortransversely stepped relative to bend lines 45. Thus, a slit, such asslit 43 a, is formed with a pair of longitudinally extending slitsegments 51 and 52 which are positioned proximate to, and preferablyequidistant on opposite sides of, and substantially parallel to, bendline 45. Longitudinal slit segments 51 and 52 are further connected by atransversely extending slit segment 53 so that slit 43 a extends fromenlarged opening 49 a to enlarged opening 49 b along an interconnectedpath which opens to both of the enlarged openings and includes bothlongitudinally extending slit segments 51, 52 and transverse slitsegment 53.

The function and advantages of such stepped slits can best be understoodby reference to FIGS. 4A-4D, and the corresponding FIGS. 5A-5C to 5A-5C,wherein the bending or folding of a sheet of material 41, such as shownin FIG. 3 is illustrated at various stages. In FIG. 4A, sheet 41 isessentially slit as shown in FIG. 3. There is a difference between FIGS.3 and 4A in that in FIG. 3 a kerf width or section of removed materialis shown, while in FIG. 4A the slit is shown without any kerf, as wouldbe produced by a slitting knife or punch. The effect during bending,however, is essentially the same if the kerf width is small enough thatthe material on the opposite sides of the slit interengage duringbending. The same reference numerals will be employed in FIGS. 4A-5C aswere employed in FIG. 3.

Thus, sheet 41 is shown in a flat condition before bending in FIG. 4A.Longitudinally extending slit-segments 51 and 52 are shown in FIG. 4Aand in the cross sections of FIGS. 5A-5C. The positions of the variouscross sections of the sheet are also shown in FIG. 4A.

In FIG. 4B, the sheet has been bent slightly along bend line 45, whichcan best be seen in FIGS. 5A-5C. As can be seen in FIGS. 5A and 5B,slits 51 and 52 have opened up along their top edges and the portion ofthe sheet which extends beyond bend line 45 was referred to in U.S. Pat.No. 6,481,259 B1 and U.S. patent application Ser. No. 10/256,870 (nowU.S. Pat. No. 6,877,349 B2) as a “tab” 55, but for the sake ofconsistency with later embodiments in this application shall be referredto as “lip” 55. The lower or bottom side edges 51 a and 52 a of lips 55have moved up slightly along supporting faces 51 b and 52 b of the sheeton the opposite sides of the slit opposite to lips 55. This displacementof lip edges 51 a and 52 a may be better seen in connection with thesheet when it is bent to a greater degree, for example, when bent to theposition shown in FIG. 4C.

In FIG. 4C it will be seen that edges 51 a and 52 a have moved upwardlyon supporting faces 51 b and 52 b of sheet 41 on opposite sides of bendline 45. Thus, there is sliding contact between edges 51 a and 52 a andthe opposing supporting faces 51 b and 52 b of the slit during bending.This sliding contact will be occurring at locations which areequidistant on opposite sides of central bend line 45 if longitudinalslit segments 51 and 52 are formed in equally spaced positions onopposite sides of bend line 45, as shown in FIG. 4A. Sliding contactalso can be facilitated by a lubricant or by adhesives or sealants priorto their setting up or bonding.

The result of this structure is that there are two actual bendingfulcrums 51 a, 51 b and 52 a, 52 b spaced at equal distances from, andon opposite sides of, bend line 45. Lip edge 51 a and supporting face 51b, as well as lip edge 52 a and supporting face 52 b, produce bending ofbending web 47 about a virtual fulcrum that lies between the actualfulcrums and will be understood to be superimposed over bend line 45.

The final result of a 90 degree bend is shown in FIG. 4D andcorresponding cross sections 5A-5C. As will be seen, sheet edge 52 a andbottom side or surface 52 c now are interengaged or rest on, and aresupported in partially overlapped relation to, supporting face 52 b(FIG. 5A). Similarly, edge 51 a and bottom surface 51 c now engages andrests on face 51 b in an overlapped condition (FIG. 5B). Bending web 47will be seen to have been plastically deformed or extended along anupper surface of the web 47 a and plastically compressed along a lowersurface 47 b of web 47, as best illustrated in FIG. 5C.

In the bent condition of FIG. 4D, the lip portions of the sheet, namely,portions 55, which extend over the center line when the sheet is slit,are now resting on supporting faces 51 b and 52 b. This edge-to-faceengagement and support during the bend, which alternates along the bendline in the configuration shown in the drawing, produces greaterprecision in bending or folding and gives the bent or folded structuregreater resistance to shear forces at the bend or fold in mutuallyperpendicular directions. Thus a load L_(a) (FIG. 5A) will be supportedbetween bending webs 47 by the overlap of the edge 52 a and bottomsurface 52 c on supporting edge 52 b. Similarly, a load L_(b) (FIG. 5B)will be supported by overlap and engagement of the edge 51 a and surface51 c on supporting face 51 b intermediate bending webs 47.

This is referred to herein as “edge-to-face” engagement and support ofthe material along substantially the entire length of one side of theslit by the material along substantially the entire length of the otherside of the slit. It will be appreciated that, if sheet 41 were bent orfolded by more than 90 degrees, edges 51 a and 52 a would lift up offthe faces 51 b and 52 b and the underneath surfaces 51 c and 52 c wouldbe supported by the lower edges of face 51 b and 52 b. If the sheet isbent by less than 90 degrees the edge still comes into engagement withthe face almost immediately after the start of bending, but only theedge engages the face. This support of one side of the slit on the othershall be deemed to be “edge-to-face” engagement and support as used inthe specification and the claims. As will be described hereinafter,non-ninety degree bends with full support of edges 51 a and 52 a byfaces 51 b can be achieved by slitting the sheet at angles which are notat 90 degrees to the sheet.

While bending straps or webs 47 have residual stresses as a result ofplastic deformation, and while the slits cause a substantial portion ofthe bend not to be directly coupled together in the slit-based bendingsystem of the present invention, the slits are formed and positioned soas to produce an edge-to-face overlap which provide s substantialadditional strength to the bent structure over the strength of thestructures of FIGS. 1, 1A and 1B and 2A and 2B, which are based uponconventional slitting or grooving geometries. The bending straps of thepresent invention, in effect, pre-load the bend so as to pull or clampthe sides of the slit into edge-to-face engagement over substantiallythe entire bending process, and at the end of the bend, oversubstantially the entire slit length. Pre-loading of the bend by theresidual tension in the strap also tends to prevent vibration betweenthe slit edge which is pre-loaded against the face which acts as a bedon the other side of the slit.

Moreover, since the edges are interengaged with the faces over asubstantial portion of the length of the slits, loads L_(a) and L_(b)will not crush or further plastically deform bending straps 47, as isthe case for the prior art slitting configuration of FIGS. 2, 2A, 2B.Loading of the present bend is immediately supported by the edge-to-faceengagement produced by the slitting technique of the present invention,rather than merely by the cross-sectional connecting area of a twistedand highly stressed strap, as results in the prior art configuration ofFIGS. 2, 2A, 2B and the Gitlin et al. application.

The embodiment employing laterally stepped or staggered slits of thepresent invention, therefore, result in substantial advantages. First,the lateral position of the longitudinally extending slit segments 51and 52 can be precisely located on each side of bend line 45, with theresult that the bend will occur about a virtual fulcrum as a consequenceof two actual fulcrums equidistant from, and on opposite sides of, thebend line. This precision bending reduces or eliminates accumulatedtolerance errors since slit positions can be very precisely controlledby a cutting device which is driven by a CNC controller.

It also should be noted, that press brakes normally bend by indexing offan edge of a sheet or an existing bend, or other feature(s). This makesbending at an angle to the sheet edge feature(s) difficult using a pressbrake. Bending precisely at angles to any feature(s) of the sheet edge,however, can be accomplished readily using the present slitting process.Additionally, the resulting bent sheet has substantially improvedstrength against shear loading and loading along mutually perpendicularaxes because the overlapped edges and faces produced by the present slitconfigurations support the sheet against such loads.

As can be seen, the embodiment of the present invention, as shown inFIGS. 3-5C produces precision bending of straps 47 which aresubstantially perpendicular to the bend line. Such an orientation of thebending straps produces significant plastic elongation along the outsideor top surface of the strap, as well as significant compression alongthe inside or bottom surface of the strap. The bend occurs on therelatively short perpendicular straps in a manner similar to the bendsof the perpendicular straps of FIGS. 1-1B, but in FIGS. 3-5C′″ the lip55 of one plane is tucked into interlocking or interengaged relationshipwith the face of the other plane for increased bend strength.

The prior art approach shown in FIGS. 2-2B orients the connecting straps34 parallel to the bend line and results in significant plastic twistingdeformation of the straps. Also this plastic twisting deformationsignificantly changes the microstructure of the material around the bendline. Moreover the straps do not fully tuck or clamp the opposite sidesof the sheet into interengaged relation over the length of the slits.Still further in the embodiment of FIGS. 3-5C′″ the strap width can bevaried independently of the jog distance between slits 51 and 52 so thatgreater flexibility in design of the bend strength can be achieved.

While bending of sheet material by 90 degrees has been illustrated inthe drawing, it will be understood that most of the advantages describedin all embodiments of the present invention also can be realized if theslit sheet is bent by more or less than 90 degrees. The lip whichextends across the bend line will slide onto and engage the oppositeface beginning at small bend angles, and such support and engagementwill continue at large, 90 degree plus, bend angles.

It has been found that the embodiment of FIGS. 3-5C′″ is best suited foruse with relatively ductile sheet materials. As the material becomesharder and less ductile, a second embodiment is preferred.

In the embodiment of the present invention shown in FIGS. 6-8B, aslitting configuration is employed which tucks or clamps the sheetmaterial into interengaged relation on both sides of the slits, and alsoreduces bending strap plastic deformation and the residual stress in thestraps. Moreover, this embodiment also allows the strap width to bevaried independently of the jog distance between slits and to have thestrap width increase in both directions from the bend line for lessstress concentration in the connected portions of the sheet of materialon opposite sides of the bend line.

A bending strap which is oblique to the bend line is employed, whichallows the strap length to be increased, as compared to the shorterbending straps of FIGS. 3-5C′″. Plastic deformation also is accomplishedin part by twisting, rather than purely by bending, as is the case inFIGS. 3-5C′″, but the amount of twisting is greatly reduced, as comparedto the parallel straps of FIGS. 2-2B. Moreover, the material lips onopposite sides of the slit are tucked into interengagement with thefaces over virtually the entire length of the slit so that substantialadditional strap stress on loading does not occur.

Additionally, in the embodiment shown in FIGS. 6-8B, the slitconfiguration produces a continuous sliding interengagement betweenmaterial on opposite sides of the slits during bending, whichinterengagement progresses along the slit from the middle toward theends. The faces on one side of the slits act as beds for sliding supportduring the bend, which results in a more uniform and a less stressfulbending of the bending straps. The embodiment as shown in FIGS. 6-8B,therefore, can be used with sheet material that is less ductile, such asheat treated 6061 aluminum or even some ceramics, and with thickersheets of material.

Referring specifically to FIGS. 6-8B, a sheet of material 241 to be bentor folded is formed with a plurality of longitudinally extending bendingstrap-defining structures, such as slits 243, along a bend line 245.Each of slits 243 optionally may be provided with enlargedstress-relieving end openings 249, or a curved end section 249 a, whichwill tend to cause any stress cracks to propagate back into slits 243,depending on the loading direction of the sheet. As will be seen, theslits of the embodiment of FIGS. 6 and 8B are not stepped, but they areconfigured in a manner producing bending and twisting of obliquelyoriented bending straps 247 about a virtual fulcrum superimposed on bendline 245. The configuration and positioning of the slits, includingselection of the jog distance and kerf width, also causes the sheetmaterial on opposite sides of the slits to tuck or to move into anedge-to-face interengaged relationship during bending. Most preferablyedge-to-face interengagement occurs throughout the bend to itscompletion. But, the jog distance and kerf can be selected to produceedge-to-face interengagement only at the start of the bend, which willtend to insure precise bending. Thus, as used herein, the expression“during bending” is meant to include edge-to-face interengagement at anystage of the bend.

While the embodiments shown and described in FIGS. 6-8B and 9-10A arenot stepped, the oblique straps of the embodiments of 6-8B and 9-10A canbe combined with the stepped slit configuration of FIGS. 3-5C. Thus, oneor both of the ends of the stepped slits can be oblique or curved. Asshown in FIG. 6, pairs of elongated slits 243 are preferably positionedon opposite sides of and proximate to bend line 245 so that pairs oflongitudinally adjacent slit end portions 251 on opposite sides of thebend line define a bending web, spline or strap 247, which can be seento extend obliquely across bend line 245. “Oblique” and “obliquely,” aswill be explained in more detail below in connection with FIG. 11, shallmean that the longitudinal central axis of the strap crosses the desiredbend line at an angle other than 90 degrees. Thus, each slit end portion251 diverges away from bend line 245 so that the center line of thestrap is skewed or oblique and bending, as well as twisting of thestrap, occurs. Although not an absolute requirement to effect bending inaccordance with the present invention, it will be seen that slits 243are longitudinally overlapping along bend line 245.

Unlike slits 31 in FIGS. 2-2B and the prior art Gitlin, et al.Application, which are parallel to the bend line in the area definingbending straps 34, the divergence of the slits 243 from bend line 245results in oblique bending straps that do not require the extremetwisting present in the prior art of FIGS. 2-2B and Gitlin et al.Application. Moreover, the divergence of slits 243 from bend line 245results in the width dimension of the straps increasing as the strapsconnect with the remainder of sheet 241. This increasing width enhancesthe transfer of loading across the bend so as to reduce stressconcentrations and to increase fatigue resistance of the straps.

As was the case for the first embodiment, slit kerfs 243 preferably havea width dimension, and the transverse jog distance across the bend linebetween slits is dimensioned, to produce interengagement of sheetmaterial on opposite sides of the slits during bending. Thus, slits 243can be made with a knife and have essentially a zero kerf, or they canhave a greater kerf which still produces interengagement, depending uponthe thickness of the sheet being bent. Most preferably the kerf width isnot greater than about 0.3 times the material thickness, and the jogdistance is not greater than about 1.0 times the material thickness.

As was the case for the embodiment of FIGS. 3-5 c, a lip portion 253extends across bend line 245 to slit 243. Lip 253 slides or rides up aface 255 of a tongue 260 on the other side of slit 243 if the kerf widthand jog distance, relative to the thickness of the material, are not solarge as to prevent contact between the two sides of the slit duringbending.

If the kerf width and jog distance are so large that contact between thelip portion 253 and face 255 of tongue 260 does not occur the bent orfolded sheet will still have some of the improved strength advantages ofoblique bending straps, but in such instances there are no actualfulcrums for bending so that bending along bend line 245 becomes lesspredictable and precise. Similarly, if the strap-defining structures aregrooves 243 which do not penetrate through the sheet of material, thegrooves will define oblique, high-strength bending straps, butedge-to-face sliding will not occur during bending unless the groove isso deep as to break-through during bending and become a slit. Thus,arcuately or divergently grooved embodiments of the bending straps willhave improved strap strength even if edge-to-face bending does notoccur.

Another problem which will be associated with a kerf width that is toowide to produce interengagement of lips 253 with faces 255 of tongues260 is that the resultant bent sheet material will not have a lip edgesupported on a slit face, unless the bend is relatively extreme so as todefine a small arcuate angle between the two sides of the bent sheet. Asnoted in connection with the prior art slitting approach, this willresult in immediate further stressing of the bending straps uponloading. The problem would not be as severe in the strap configurationof FIGS. 6-8B as in the prior art, but the preferred form is for thekerf width and jog distance to be selected to insure interengagement ofthe lip and tongue face substantially throughout the bending process.

It is also possible for the slits 243 to actually be on the bend line oreven across the bend line and still produce precise bending from thebalanced positioning of the actual fulcrum faces 255 and the edges oflips 253 sliding therealong. A potential disadvantage of slits 243 beingformed to cross the bend line 245 is that an air-gap would remainbetween edge 257 and face 255. An air-gap, however, may be acceptable inorder to facilitate subsequent welding, brazing, soldering, adhesivefilling or if an air-gap is desired for venting. Slit positioning tocreate an air-gap is a desirable feature of the present invention whensubsequent bend reinforcement is employed. Unfilled, however, an air-gapwill tend to place all of the load bearing requirements of the bend inall degrees of freedom, except rotation, on the connected zone orcross-sectional area of plastically deformed strap 247. It is alsopossible to scale slits that cross the bend line that produceedge-to-face engagement without an air gap.

FIGS. 7, 8, 8A and 8B illustrate the sheet 241 as bent to a 90 degreeangle along bend line 245. As best may be seen in FIGS. 8A and 8B, aninside edge 257 of lip 253 has slid up on face 255 of tongue 260 on theopposite side of the slit and is interengaged and supported thereon. Avertical force, F_(v), therefore, as shown in FIG. 8A is supported bythe overlap of edge 257 on face 255. A horizontal force, F_(H), as shownin FIG. 8B similarly will be resisted by the overlap of edge 257 on face255. Comparison of FIGS. 8A and 8B to the prior art FIGS. 1A, 1B and 2Aand 2B will make apparent the differences which the present bendingmethod and slit configuration have on the strength of the overallstructure. The combination of alternating overlapping edge-to-facesupport along the slits and the oblique bending straps, which areoblique in oppositely skewed directions, provides a bend and twist whichis not only precise but has much less residual stress and higherstrength than prior slitting configurations will produce.

However, skewing of the bending straps in opposite directions is notrequired to achieve many of the advantages of the present invention.When sheet 241 is an isotropic material, alternate skewing of the straplongitudinal central axes tends to cancel stress. If the sheet materialis not isotropic, skewing of the oblique straps in the same directioncan be used to negate preferential grain effects in the material.Alternatively, for isotropic sheet material, skewing of the straps inthe same direction can produce relative shifting along the bend line ofthe portions of the sheet on opposite sides of the bend line, whichshifting can be used for producing a locking engagement with a thirdplane such as an interference fit or a tab and slot insertion by theamount of side shift produced.

The geometry of the oblique slits is such that they bend and twist overa region that tends to reduce residual stress in the strap material atthe point where the slit is terminated or the strap connected to therest of the sheet. Thus, crack propagation is reduced, lessening theneed for enlarged openings or curls at the slit ends. If the resultantstructure is intended primarily for static loading or is not expected tobe loaded at all, no stress reducing termination is required in thearcuate slit that produces the oblique strap.

Moreover, it will be understood that slits 243 can be shifted along bendline 243 to change the width of straps 247 without increasing jogdistance at which the slits are laterally spaced from each other.Conversely, the jog distance between slits 243 can be increased and theslits longitudinally shifted to maintain the same strap thickness.Obviously both changes can be made to design the strap width and lengthto meet the application.

Generally, the ratio of the transverse distance from slit to slit, ortwice the distance of one slit to the bend line is referred to as the“jog”. The ratio of the jog distance relative to the material thicknessin the preferred embodiments of the present invention will be lessthan 1. That is, the jog distance usually is less than one materialthickness. A more preferred embodiment makes use of a jog distance ratioof less than 0.5 material thickness. A still more preferred embodimentmakes use of a jog distance ratio of approximately 0.3 materialthickness, depending upon the characteristics of the specific materialused and the widths of the straps, and the kerf dimensions.

The width of bending straps 247 will influence the amount of forcerequired to bend the sheet and that can be varied by either moving slits243 farther away from the bend line 245 or by longitudinally shiftingthe position of the slits, or both. Generally, the width of obliquebending straps 247 most preferably will be selected to be greater thanthe thickness of the material being bent, but strap widths in the rangeof about 0.5 to about 4 times the thickness of the material may be used.More preferably, the strap width is between 0.7 and 2.5 times thematerial thickness.

One of the advantages of the present invention, however, is that theslitting configuration is such that bending of sheets can normally beaccomplished using hand tools or tools that are relatively low powered.Thus, the bending tools need only so much force as to effect bending andtwisting of bending straps 247; they do not have to have sufficientpower so as to control the location of the bend. Such control isrequired for powered machines, such as press brakes, which clamp thematerial to be bent with sufficient force so as to control the locationof the bend. In the present invention, however, the location of the bendis controlled by the actual fulcrums, namely edges 257 pivoting on face255 on opposite sides of the bend line. Therefore, the bending toolrequired need only be one which can effect bending of straps 247, notpositioning of the bend. This is extremely important in applications inwhich high strength power tools are not readily available, for example,in outer space or in the field fabrication of structures or atfabricators who do not have such high-powered equipment. It also allowslow-force sheet bending equipment, such as corrugated cardboard bendingmachines, bladders, vacuum bending, hydraulic pulling cylinders withfolding bars, and shape-memory bending materials, to be used to bendmetal sheets, as will be set forth in more detail below. Additionally,strong, accurate bends are important in the fabrication of structures inwhich physical access to power bending equipment is not possible becauseof the geometry of the structure itself. This is particularly true ofthe last few bends required to close and latch a three-dimensionalstructure.

The most preferred configuration for slit end portions 251 is an arcuatedivergence from bend line 245. In fact, each slit may be formed as acontinuous arc, as shown in FIGS. 9, 10 and 10A and described below. Anarc causes the material on the side of the slit to smoothly andprogressively move up the face side of the tongue along an arcuate pathbeginning at center of the slit and progressing to the ends of the slit.This reduces the danger of hanging up of edge 257 on face 255 duringbending and thereby is less stressful on the bending straps.Additionally, large radii of cut free surfaces are less prone to stressconcentration. In the configuration of FIGS. 6-8B, the central portionof slits 243 is substantially parallel to bend line 245. Somenon-parallel orientations, particularly if balanced on either side ofthe bend line, may be acceptable and produce the results describedherein.

It also would be possible to form end portions 251 to diverge from bendline 245 at right angles to the bend line and the center of slits 243.This would define a bending strap that could be non-oblique, if theslits did not longitudinally overlap. The disadvantage of this approachis that the bending straps 247 tend not to bend as uniformly andreliably and thereby influence the precision of the location of thebend. Additionally, such a geometry eliminates twisting of the strap andinduces severe points of stress concentration on the inner and outerradii of the bend and may limit the degree of edge-to-edge engagement.

The bending straps in all the embodiments of the present invention arefirst elastically deformed and in plastic/elastic materials thereafterplastically deformed. The present slitting invention also can be usedwith elastically deformable plastics that never plastically deform. Suchmaterials would be secured in a bent or folded condition so that they donot resiliently unbend. In order to make it more likely that onlyelastic deformation occurs, it is preferable that the bending straps beformed with central longitudinal strap axes that are at a small angle tothe bending line, most preferably, 26 degrees or less. The lower theangle, the higher the fraction of twisting that occurs and the lower thefraction of bending that occurs. Moreover, the lower the angle, thehigher the bending radius that occurs. Rigid materials that do notgracefully deform plastically, such as rigid polymers, rigid metal, themore flexible ceramics and some composites, can tolerate a large bendingradius in the elastic regime. They can also tolerate a torsion ortwisting spring action that is distributed over a long strap ofmaterial. Low angle straps provide both aspects.

At the end of the bend of a plastically deformed sheet, however, therewill remain a certain resilient elastic deformation tending to pull edge257 down against face 255 and resulting in residual resilient clampingforce maintaining the interengagement between material on opposite sidesof the slits. Thus, the elastic resiliency of the sheet being bent willtend to pre-load or snug down the overlapping sheet edges against thesupporting faces to ensure strength at the bend and reduce bending strapincremental stress on loading of the bend.

The embodiment shown in FIGS. 9, 10 and 10A is a special case of theoblique strap embodiment described in connection with FIGS. 6-8B. Herethe oblique straps are formed by completely arcuate slits 443. This slitconfiguration, shown as a circular segment, is particularly well suitedfor bending thicker and less ductile metal sheets, for example, titaniumand ¼ inch steel plate and up.

When arcuate or circular slits 443 are formed in sheet 441 on oppositesides of bend line 435, lip portions 453 of the sheet, which extend overbend line 445 to slits 443, begin tucking or sliding onto face 455 ofthe tongues 470 at a center of each arcuate slit at the start ofbending. Lip portions 453 then slide from the center of each slitpartially up onto tongue faces 455 progressively toward the slit ends asstraps 447 are twisted and bent. The progressive tucking of the lipsonto the opposing faces is less stressful on the slit ends 449, andtherefore more suitable for bending of less ductile and thickermaterials, than say the embodiment of FIGS. 6-8B, in which the slitshave straight central portions and simultaneously slide up onto thefaces over the entire straight portion.

Slit ends 449 in FIG. 10 do not have the stress-relieving openings 249,nor radiused ends 249 a of FIGS. 6-8 nor the curved ends of FIG. 11, butslits 443 are more economical to cut or form into most sheet stock.Moreover, the deformation of straps 447 is more gradual during bendingso that stress concentration will be reduced. This, of course, combineswith increasing strap width to transfer loading forces and bendingforces more evenly into the remainder of the sheet with lower stressconcentration.

The various embodiments of the present sheet slitting and groovinginvention allow designing manufacturing and fabrication advantages to beachieved which have not heretofore been realized. Thus, the fullbenefits of such design and fabrication techniques as CAD design, RapidPrototyping and “pick and place” assembly can be realized by using sheetstock formation techniques in accordance with the present invention.Moreover, standard fabrication techniques, such as welding, are greatlyenhanced using the strap-defining configurations of the presentinvention.

The many advantages of using sheets formed in accordance with thepresent invention can be illustrated in connection with a manufacturingtechnique as basic as welding. Sheet bending using the present method,for example, avoids the manufacturing problems associated with handlingmultiple parts, such as jigging.

Additionally, the bent sheets of the present invention in which slittingis employed can be welded along the slits. As can be seen in FIG. 10A,for example, face 455 and end surface 457 of tab 453 form a V-shapedcross section that is ideal for welding. No grinding or machining isrequired to place a weld 460 (broken lines) along slits 443 as shown inFIG. 10A. Moreover, the edge-to-face engagement of the sides of thesheet on opposite sides of the slits, in effect, provides a jig orfixture for holding the sheet portions together during the weld and forreducing thermally induced warping. Set up time is thereby greatlyreduced, and the dimensional accuracy achieved by the present slittingprocess is maintained during the welding step. The arcuate slits alsoprovide an easily sensed topographic feature for robotic welding. Theseadvantages also accrue in connection with soldering, brazing andadhesive filling, although thermal distortion is usually not a seriousissue for many adhesives.

Filling of the slits by welding, brazing, soldering, potting compound oradhesives allows the bent sheets of the present invention to be formedinto enclosures which hold fluids or flowable materials. Thus, bentsheet enclosures can even be used to form fluid-tight molds, with thesheeting either being removed or left in place after molding.

One of the significant advantages of using oblique, and particularlycurved, grooves or slits is that the resulting bending straps arediverging at the point at which they connect to the reminder of thesheet material. Thus, area 450 of strap 447 in FIG. 10 is transverselydiverging between slit end 449 and the next slit 443. This divergencetends to deliver or transfer the stresses in strap 447 at each end intothe remainder of the sheet in a diffused or unconcentrated manner. Asthe arc or radius of the slits is reduced the divergence increases,again allowing a further independent tailoring of the strap stresstransfer across the bend. Such tailoring can be combined with one ormore of changes to strap width, jog distance and slit kerf to furtherinfluence the strength of the bend. This principle is employed in thedesign of the slits on grooves of FIG. 11.

While the oblique bending straps of the embodiments of FIGS. 6-8 andFIGS. 9-10 result in substantial improvements of the overall strengthand fatigue resistance of the bent structure, it has been foundempirically that still further improvements, particularly in connectionwith fatigue, can be achieved if the strap-defining structure takes theform of an arcuate slit. As used herein, “arcuate” shall mean andinclude a circular arc and a series of longitudinally connected,tangential arcs having differing radii. Preferably, the arcuate slits orgrooves have relatively large radii (as compared to the sheetthickness), as illustrated in FIG. 11. Thus, a sheet of material 541 canbe provided with a plurality of connected, large radii, arcuate slits,generally designated 542, along bend line 543. Arcuate slits 542preferably are longitudinally staggered or offset (by an offset distancemeasured between the centers of adjacent slits along bend line 543 andalternatively are on opposite sides of the bend line 543, in a mannerdescribed above in connection with other embodiments of the presentinvention. Arcuate slits 542 define connected zones, which are bendingstraps 544, and disconnected zones, which are provided by slits 542.Only the right hand slit 542 in FIG. 11 shows a kerf or slit thickness,with the remainder of the slits 542 being either schematically shown ortaking the form of a slit form by a knife resulting in no kerf.

Longitudinally adjacent slits 542 defined therebetween bending straps544, which are shown in this embodiment as being oblique to bending line543 and skewed in alternating directions, as also described above. Eachslit 542 tends to have a central arcuate portion 546 which diverges awayfrom bending line 543 from a center point 547 of the arcuate slit. Endportions 548 also may advantageously be arcuate with a much smallerradius of curvature that causes the smiles to extend back along arcportion 549 and finally terminated in an inwardly arc portion 551.

It will be seen, therefore, that bending strap 544 is defined by the arcportions 546 on either side of bending line 543 and at the end of thestraps by the arcuate end portions 548. A minimum strap width occursbetween the arcuate slit portions 546 at arrows 552 (shown in FIG. 11 atthe left hand pair of longitudinally adjacent slits). If a center line553 is drawn through arrows 552 at the minimum width of the strap, itwould be seen that the center line crosses bend line 543 at about theminimum strap width 552. Strap 544 diverges away from longitudinal strapaxis 553 in both directions from minimum strap width 552. Thus, aportion 554 of the sheet on one side of bend line 543 is connected to asecond portion 556 of the sheet on the opposite side of bend line 543 bystrap 544. The increasing width of strap 544 in both directions from theminimum width plane 552 causes the strap to be connected to therespective sheet portions 554 and 556 across the bend line in a mannerwhich greatly reduces stress and increases fatigue resistance.

For purposes of further illustration, strap 544 a has been cross hatchedto demonstrate the increasing width of the strap along its centrallongitudinal strap axis 553. Coupling of sheet portion 554 by anever-increasing strap width to sheet portion 556 by a similarlyincreasing strap width tends to reduce stress. Orienting the centrallongitudinal axes 553 of straps 554 at an oblique angle to bend line 543results in the straps being both twisted and bent, rather than solelytwisted, which also reduces stresses in the straps. Stresses in thesheet flow across the bend through the connected material of the strap.Cyclical stress in tension, the primary cause of fatigue failure, flowthrough the twisted and bent strap and generally parallel to large radiiarcs 546 and 549. The smaller radii of arcs 551 and 548 provide a smoothtransition away from the primary stress bearing free surfaces of 546 and549 but do not themselves experience significant stress flow. In thisway, the arcuate slits are like portions of very large circles joinedtogether by much smaller circles or arcs in a way that positions onlythe large radii arcs (compared to the material thickness) in the stressfield flow, and uses smaller radii arcs as connectors to minimize thedepth into the parent plane away from the fold line that the slit isformed. Thus, slit ends, at which stress caused micro cracking is mostlikely to occur, will tend not to be propagated from one slit to anotherdown the length of the bend, as can possibly occur in a failurecondition in the embodiments of FIGS. 6-8 and 9-10.

The bending strap shape also will influence the distribution of stressesacross the bend. When the bending strap diverges relatively rapidly awayfrom the narrowest strap width dimension, e.g., width dimension 552 inFIG. 11, there is a tendency for this minimum dimension to act as awaist or weakened plane at the center of the strap. Such rapid narrowingwill allow localized plastic deformation and stress concentration in thestrap, rather than the desired distribution of the stresses over thefull length of the strap and into the sheet material 554 and 556 oneither side of the strap.

As shown in FIG. 11, and as is preferred, strap 544 preferably a minimumwidth dimension 552 providing the desired strap strength and thengradually diverge in both directions along the strap with any rapiddivergence taking place as the strap terminates into the sheet portions554 and 556. This construction avoids the problem of having an undulynarrow strap waist at 552 which will concentrate bending and twistingforces and produce failure, rather than distributing them evenly alongthe length of the strap and into sheet portions 554 and 556.

The tongue side of a slit, that is, the portion of the parent planedefined by the concave side of the arcuate slit, tends to be isolatedfrom tensile stress. This makes the tongue ideal for locating featuresthat cut into the parent plane. Attachment or alignment holes, ornotches that mate with other connecting geometry are examples. FIG. 11Aillustrates positioning of water-jet cut or laser cut, rapid piercingholes 560 and 565 on the tongue 555 of slit 546. Rapid pierce holes aresomewhat irregular and elsewhere might initiate a crack failure infatigue. In FIG. 11A two alternative locations of rapid piercing holesare shown. Rapid pierce holes are important to reduce the total cost oflaser or water-jet cutting because slow piercing is very time consuming.

One of the most beneficial aspects of the present invention is that thedesign and cutting of the material to form the straps and theedge-to-face engagement of the lips and tongues of the slits isaccomplished in a manner in which the microstructure of the materialaround the bend or fold is essentially unchanged in comparison to thesubstantial change in the microstructure of materials bent or folded tothe same angle or degree of sharpness using conventional bendingtechniques, as described in the prior art. It is the relationship of thestraps and the edge-to-face engagement of the slits which provides acombination of twisting and bending deformation when the material isbent that greatly reduces the stress around the bend and leaves themicrostructure of the material around the bend essentially unchanged.When conventional bending techniques of the prior art are used there isa substantial change in the microstructure of the material around thebend if the bend is made to be sharp (for example, 90 degrees on theinside of the bend, as shown for example in FIGS. 5A, 8, 8A, 8B and 10A.

As was generally described in connection with other embodiments of thepresent invention, slits 542 can have their geometries altered toaccommodate a wide range of sheet characteristics. Thus, as the type ofsheet material which is bent is altered, or its thicknesses changed orstrength characteristics of the bend are to be tailored, the geometry ofsmile slits 542 can also change. The length, L, of each slit can change,as can its offset distance, O.D., or longitudinal spacing along bendline 543. The height, H, of the slits can also be changed, and the jogdistance, J, across the bend line between slits on opposite sides of thebend line can be altered. These various factors will have an effect onthe geometry and orientation of straps 544, which in turn will alsoeffect the strength of the bend and its suitability for use in variousstructures. Of equal importance is the shape of the arcuate slit inconjunction with the aforementioned sealing and positioning variable.

It is a feature of the present invention, therefore, that thestrap-defining slits or grooves can be tailored to the material beingbent or folded and the structure to be produced. It is possible, forexample, to empirically test sheets of a given material but havingdiffering thicknesses with arc slit designs in which the geometries havebeen changed slightly, but the designs comprise a family of related arcgeometries. This process can be repeated for differing materials, andthe empirical data stored in a database from which designs can beretrieved based upon input as to the sheet of material being bent andits thickness. This process is particularly well suited for computerimplementation in which the physical properties of the sheet of materialare entered and the program makes a selection from the computer databaseof empirical data as to the most appropriate arc geometry for use inbending the material. The software can also interpolate betweenavailable data when the sheet is of a material for which no exact datais stored or when the sheet has a thickness for which there are no exactstored data.

The design or configuration of the arcs, and thus the connecting straps,also can be varied along the length of a bend line to accommodatechanges in the thickness of the sheet of material along the bend line.Alternatively, strap configurations along a bend line can change or betailored to accommodate non-linear loading. While not as important asthe strength and fatigue-resistance improvements of the presentinvention, the slit or strap configurations also can be varied toprovide different decorative effects in combination with improvedstrength and fatigue resistance.

Another advantage which accrues from the various embodiments of thesheet slitting system of the present invention is that the resultingbends or fold are relatively sharp, both internally and externally.Sharp bends enable strong coupling of one bent structure to anotherstructure. Thus, a press brake bend tends to be rounded or have anoticeable radius at the bend. When a press brake bent structure iscoupled to a plate, for example, and a force is applied tending torotate the bent structure about the arcuate bend, the bent structure candecouple from the plate. Such decoupling can occur more easily than ifthe bend were sharp, as it will be for the bends resulting from usingthe present slitting scheme.

The ability to produce sharp or crisp bends or folds allows the processof the present invention to be applied to structures which hadheretofore only been formed from paper or thin foils, namely, to thevast technology of origami or folded paper constructions. Complexthree-dimensional folded paper structures, and a science or mathematicsfor their creation, have been developed after centuries of effort. Suchorigami structures, while visually elegant, usually are not capable ofbeing formed from metal sheets of a thickness greater than a foil. Thus,origami folded sheets usually cannot support significant loading.Typical examples of origami are the folded paper constructions set forthin “ADVANCED ORIGAMI” by Dedier Boursin, published by Firefly Books,Buffalo, N.Y. in 2002, and “EXTREME ORIGAMI” by Kunihiko Kasahara,published by Sterling Publishing Company, NY, N.Y. in 2002. The presentinvention thus enables a new class of origami-analog designs in whichthe slitting and bending methods described herein are substituted fororigami creases.

The sheet slitting or grooving process of the present invention producessharp bends and even allows the folding of metal sheets by 180 degreesor back on itself. Thus, many structurally interesting origamiconstructions can be made using sheet metal having a thickness wellbeyond that of a foil, and the resulting origami-based structure will becapable of supporting significant loads.

Another interesting design and fabrication potential is realized byusing the present slitting configurations in connection with RapidPrototyping and Rapid Manufacturing, particularly if automated “Pick andPlace” component additions are employed. Rapid Prototyping and RapidManufacturing are broadly known and are comprised of the use of CAD(computer-assisted design) and CAM (computer-assisted manufacturing)design, respectively, to enable three-dimensional fabrication. Thedesigner begins with a desired virtual three-dimensional structure.Using the current invention to enable Rapid Prototyping, the CADsoftware unfolds the three-dimensional structure to a two-dimensionalsheet and then locates the slit positions for bending of the sheet toproduce the desired structure. The same can be done in RapidManufacturing using CAM. Other types of software for performing similartasks. The ability to precisely bend, and to tailor the bend strength,by selecting jog distances and bending strap widths, allows the designerto layout slits in the unfolded two-dimensional sheet drawing in thedesign process, which thereafter can be implemented in the manufacturingprocess by sheet grooving or slitting and bending to produce complexthree-dimensional structures, with or without add-on components.

Broadly, it is also known to assemble components onto circuit boards forelectronic devices using high speed “pick and place” automated componenthandling techniques. Thus, assembly robots can pick components fromcomponent supply devices and then place them on a circuit board orsubstrate or chassis. The robotics secure the components to thesubstrate using fasteners, soldering plug-ins or the like. Such “pickand place” assembly has been largely limited to placing the componentson a flat surface. Thus, the circuit boards must be placed in athree-dimensional housing after the “pick and place” assembly has beencompleted.

An electronic housing, usually cannot be folded or bent into athree-dimensional shape after components are secured to the walls of thehousing. Moreover, prior techniques for bending have lacked theprecision possible with the present invention and necessary to solvecomponent or structural alignment problems. Pre-folding or bending upthe housing has, therefore, limited the ability for pick and placerobotics to be used to secure electronic components in the housings.

It also should be noted that the straps present between slits can beadvantageously used as conductive paths across bends in electronicapplications, and the precision possible allows conductive paths orcomponents on the circuit board to be folded into alignment when thethree-dimensional chassis is formed, or when circuit boards themselvesare folded into a more dense conformation.

The design and manufacturing processes of the present invention,however, enable precision bends to be laid out, slit and then formedwith relatively low forces being involved, as is illustrated in FIGS.28A-28E. Thus, a housing can be designed and cut from a flat sheet 821and high-speed pick and place robotics used to rapidly securecomponents, C, to any or all six walls of a cube enclosure, and thehousing or component chassis can be easily bent into a three-dimensionalshape after the pick and place process is completed.

As shown in FIG. 28A, sheet 821 has component C secured thereto beforebending, preferably by high-speed robotic techniques. Sheet 821 isformed by laser cutting, water jet cut, die cutting or the like with thedesigned cutout features 822, component-receiving openings 823, tabs 824and support flanges 826 and tab-receiving slots 827. In FIG. 28B sheet821 has been bent along bend line 831, causing a tab 824 to be displacedoutwardly. The sheet is next bent along bend line 832 in FIG. 28C andthen bent over component C along bend line 833 in FIG. 28D, while sideflange 826 has been bent along bend line 834. Finally, chassis endportion 836 is bent upwardly along bend line 837 and tabs 824 areinserted into slots 827 so as to enable rigid securement of the sheetinto a three-dimensional electronics chassis 838 around component C.

Obviously, in most cases a plurality of components C would be secured tosheet 821 before bending, and components C also can be secured tochassis 838 at various steps in the bending process and to varioussurfaces of the chassis.

FIGS. 28A-28E also illustrate a fundamental design process which isimplemented by the sheet bending method of the present invention. One ofthe most space-efficient ways of supporting components is to mount themon sheet stock. Using conventional sheet stock bending techniques,however, does not enable tight bends and intricate inter-leaved sheetportions. The bending process of the present invention does, however, byreason of the ability to lay out slits extremely accurately that willproduce bend in precise locations so that openings, cutouts, slots, tabsand the like will precisely align in the bent structure, as well asmounted components and the coupling to other structures.

Moreover, the precise layout of bending lines and chassis or enclosurefeatures is only part of the advantage. The structure itself can be bentusing relatively low force, and even by means of hand tools. Thecombination of precision location of bend lines and low-force bendingenables a design technique which was only heretofore partially realized.The technique involves selecting components having the desired functionsand positioning them in space in a desired arrangement. Thereafter, achassis is designed with supporting thin sheet portions of the chassisnecessary to support the components as positioned being designed, forexample, using CAD techniques. The bend lines are located to produce thesupporting sheet portions, and the chassis unfolded graphically to aflat sheet with the necessary feature and fold lines, as shown in FIG.28A.

While such techniques have been described before in CAD designliterature, and CAD and CAM software programs, they have not heretoforebeen effectively implemented in anything but the most simple designsbecause precision, low-force bending of sheet metals was not practical.The present slitting-based invention enables practical fabrication ofthis theoretical CAD or CAM design technique. Prior art CAD or CAMdesigns could not previously be physically realized in real materials tothe same accuracy as the theoretical CAD or CAM model because, forexample, conventional bending tolerances could not be held. Theprecision of bending possible with the present invention dramaticallyincreases the correspondence between the CAD or CAM model and theachievable physical form for bent sheet materials.

Moreover, the bending need not take place at the pick and place or rapidprototyping site. The sheet with attached components can be transportedwith the components being formed and selected to act as dunnage for thetransport process. Once at the fabrication site, which may be remotefrom the design and cutting site, the chassis or housing sheet will bebent precisely, even by hand if desired, and the bent housing securedinto a three-dimensional structure, with a plurality of selectedcomponents being secured thereto internally and/or externally.

Moreover, three-dimensional chassis and other structures also can havepanels therein which are attached by straps along a bend line to providedoors in the chassis or structure for periodic or emergency access tothe interior of the structure. Separate door hinge assemblies arethereby eliminated.

Using the various embodiments of the sheet slitting or groovingtechniques described herein, an extremely wide range of products can beformed. Without limitation by enumeration, the following are examples ofproducts which can be folded from sheet material using the slitting andgrooving schemes of the present invention: trusses, beams, curved beams,coiled beams, beams within beams, enclosures, polyhedrons, stud walls,beam networks, enveloped beams, flanged beams, indeterminatemultiple-piece flanged beams, machines, works of art and sculpture,origami three-dimensional structures, musical instruments, toys, signs,modular connections, packages, pallets, protective enclosures,platforms, bridges, electrical enclosures, RF shield enclosures, EMIshields, microwave guides and ducts. A few examples of such structuresare shown in FIGS. 12-30 and 32.

Formation of a curved box beam using the slitting process and slit sheetof the present invention can be described by reference to FIGS. 12, 13and 14. A sheet of material 561 is shown in FIG. 12 that has two bendlines 562 and 563. Bend line 562 has a plurality of arcuate slits 563 onopposite sides of bend line 562. Also positioned along bend line 562 aresmaller arcuate slits 564. The slits 563 and 564 have the generalconfiguration as described and shown in connection with slits 542 inFIG. 11, but the length of slits 564 is reduced relative to the lengthof slits 563, and slits 564 will be seen to be positioned at the apex566 of notches 567 which are provided in the edges 568 of the sheet ofmaterial. The bending straps 569 defined by longitudinally adjacent endportions of slits 563 and longitudinally adjacent end portions of slits563 and 564 are essentially the same in configuration, notwithstandingdifferences in the length of the slits 563 and 564. There will be someslight shape difference due to arcuate segment differences, but bendingstraps 569 will be essentially uniform in their strength andfatigue-resistant capabilities along the length of bending line 562.

One of the advantages of the placement of slits 564 is that they tend tocontain any stress crack propagation, which could occur at apexes 566 ofnotches 567. The various leaves or fingers 571 defined by notches 567can be bent, for example, into or out of the page to a 90 degree angle,or to other angles if the structure should require. The central portion572 can remain in the plane of the sheet on which FIG. 12 is drawn.

A plurality of slits 576 and 577 are positioned along second bendingline 563. These slits have much tighter end curve portions 578 than thearc-like slits shown proximate first bend line 562. Generally, the tightcurved end portions 578 are not as desirable as the more open-endedportions used in connection with slits 563 and 564. Nevertheless, forductile materials that do not tend to stress fracture, slits of the typeshown for slits 576 and 577 are entirely adequate. Again, the differencebetween slits 576 and 577 is that the smaller slits have been used atthe apexes 566 of notches 567.

Once slit, sheet 561 can be bent along bend line 563 so that the leaves571 can be bent to an angle such as 90 degrees relative to the centralportion 572. It should be noted that normally the slits along bend line562 and 563 will have the same shape, that is, they will either be slits563 and 564 or slits 576 and 577. It is possible to mix slitconfigurations, but normally there will be no advantage from mixing themas shown in FIG. 12. The purpose of the illustrated embodiment of FIG.12 is to show different slit configurations that are suitable for use inthe bending of sheet material in accordance with the present invention.

The design and formation of a curved box beam using two sheets slit, asshown in the flat in FIG. 12, can be described in connection with FIGS.13 and 14. The design would be accomplished on a CAD or CAM system, asdescribed earlier, and the slits made in sheet 561 identically as laidout in the design process on the CAD, CAM or other systems. A curved boxbeam, generally designated 581, is shown in which one designed, cut andbent U-shaped sheet 572 a is secured to a second designed, cut and bentU-shaped sheet 572 b. As will be seen from FIGS. 13 and 14, the fingersor leaves 571 a have been folded down over the outside of the fingers orleaves 571 b. In both cases, the apexes 566 are closely proximate thefold lines 562 a, 563 a, 562 b and 563 b. This placement of the apexesallows bending of the sheet, by permitting notches 567 a to have theincluded angle of the notches increase, while the included angle ofnotches 567 b decrease in the area 582 of the longitudinal bending ofbeam 581. The central portions 572 a and 572 b of the sheet materialhave a thickness that will accommodate bending without buckling, atleast in radii that are not extreme.

The folded sheets can be secured together by rivets 583 or othersuitable fasteners, adhesives or fastening techniques such as weldingand brazing. Openings for the fasteners can be pre-formed as shown inFIG. 12 at 580. The location of the openings 580 can be precisely set ifthe exact curved configuration is determined or known in advance ofbending, or openings 580 can be positioned in central locations andthereafter used with later drilled holes to join the two bent sheetstogether in a curvature that is indeterminate or established in thefield.

One application for indeterminate curved box beams, for example, is inthe aircraft industry. Difficult to bend 4041 T-6 or 6061 T-6 aluminumis designed with the desired layout of slits and then provided incompleted slit sheets as shown in FIG. 12. The sheets are then formed inthe field to provide a box beam having a curvature which is determinedin the field, for example, by the curvature of a portion of an airplanewhich must be repaired. The two sheets that form the box beam are curvedto fit under a portion of the skin of the airplane which has beendamaged, and then the skin is thereafter attached to the central section572 of the curved box beam.

Bending of the leaves or fingers 571 can be done with simple hand tools,or even by hand, and field riveting used to hold the curvature of thebox beam by using the pre-formed holes 58 as guides for holes that aredrilled in the leaves or fingers of the underlying folded sheet. Thus,with a simple hand drill and pliers, a high-strength structural 4041 T-6aluminum box beam can be custom formed and positioned as an airplanestructural component for subsequent fastening of the skin of theairplane thereto. This can enable, for example, field repairs under evencombat conditions so that the plane can be flown to a site at whichpermanent repairs can be made.

When the longitudinally curved box beam has a predetermined or knownlongitudinal curvature, leaves or fingers 571 a and 571 b can be definedby notches in which the fingers interdigitate or mesh with each other inthe same plane. This will produce beam side walls that are smooth andwithout openings.

As shown in FIGS. 12-14 a longitudinally curved box beam 681 is producedby bending the sheet material along straight fold lines 562 and 563. Itis also possible to produce a longitudinally curved box beam by slittingor grooving along curved bend lines. “Longitudinally” refers to adirection transverse to the bend line and/or original plane of the sheetas shown, for example, in FIGS. 13-14. “Longitudinal bend” refers tobending in a transverse direction to a bend line and is generally usedinterchangeably with “longitudinal curvature.”

In addition to the curved beam embodiments described above, otherexamples of curved structural members are immediately apparent as aresult of simply laying out bending strap-defining structures along bendlines having non-linear portions. On folding or bending along such bendlines, or curves, the sheet becomes a curved three-dimensionalstructure.

Turning now to FIGS. 15 and 16, a sheet of material designed and slit orgrooved for folding and a three-dimensional structure made from thesame, respectively, are shown. Sheet 611 has been designed to be slit orgrooved along longitudinally extending fold lines 612 and 613. Furtherslitting and grooving has taken place on transversely extending foldlines 614, 615, 616 and 617. Opposed side edges 618 of sheets 611 arecircular, and a plurality of notches 619 are formed in opposite sideedges of the sheet. A coupling tab or flange 621 is formed at one end ofthe sheet and preferably has fastener receiving openings 622 thereinwhich will align with opening 623 in the opposite end of sheet 611.Slits or grooves 624 of the type shown in the embodiment of FIGS. 9 and10 have been positioned along fold lines 612-617. It will be understoodthat slits or grooves of the type shown in other embodiments could beemployed within the scope of the present invention.

The sheet of material shown in FIG. 15 is designed to envelop or enclosea cylindrical member, such as a rod, post or column 631 shown in FIG.16. By bending sheets 616 along fold lines 612-617, sheet 611 can befolded around to enclose cylindrical member 631 as shown in FIG. 16. Thecircular arcuate portion 618 of the sheet are dimensioned to have aradius which mates with that of column 631. Notches 619 close up and theedges defining the notches abut each other, while the fold lines 614-617allow the sheet to be folded into a square configuration around thecolumn 631. The bent three-dimensional structure which results has aplurality of planar panels 636-639 which provide surfaces against whichother members or structures can be easily attached. Folded sheet 611 maybe secured in place around column 631 by fasteners through openings 622and 623. The configuration of the grooves or slits 624 causes the foldedsheet 611 to become a high-strength, rigid structure around column orpost 631. Securement of folded sheet 611 to post 631 against verticaldisplacement can be the result of an interference fit between arcuateedges 618 and the post, and/or the use of fasteners, adhesives, welding,brazing or the like, and the assembly has many applications which solvethe problem of subsequent coupling of structural members to acylindrical structure. The example of FIGS. 15 and 16 is not only apotential cosmetic cladding, it is a structural transition piece betweencylindrical and rectilinear forms.

The designed and manufactured slit or grooved sheet and method of thepresent invention also may be used to design and form corrugated panelor deck assemblies. FIGS. 17 and 18 illustrate two corrugated panelassemblies that can be designed and constructed using the apparatus andmethods of the present invention. Such assemblies are particularlyeffective in providing high-strength-to-weight ratios, and the sheetfolding techniques of the present invention readily accommodate bothfolding of the corrugated sheet and the provision of attachment tabs.

In FIG. 17 attachment tabs are provided which can extend through slitsto couple the corrugated sheet to the planar sheet, while in FIG. 18tabs having fastener receiving openings are provided.

In FIG. 17, a sheet of material 641 has been slit or grooved alonglongitudinally extending fold lines 642-647 in accordance with theteaching of the present invention. Additionally, a plurality of tabs 649have been formed along fold line 643, 645 and 647. Tabs 649 are cut insheet 641 at the same time as formation of the slits or grooves 651along the fold lines. Thus, a U-shaped cut 652 is formed in sheet 641 sothat when the sheet is folded to the corrugated condition shown in FIG.17, the tabs will protrude upwardly. Tabs 649 will extend at an anglefrom the vertical when folding occurs to form the corrugations, but tabs649 can be bent from an angled position to a near vertical position, asshown in 617, by a subsequent step.

The folded or corrugated sheet 641 shown in FIG. 17 can be attached to asecond planar sheet 656 which has a plurality of slits 657 formedtherein. Slits 657 are positioned and dimensioned to matingly receivetabs 649 therethrough. When sheet 656 is lowered down over corrugatedfolded sheet 641, tabs 649 will extend up through slits 657. Tabs 649can be in interference fit with slits 657 to secure the sheets together,or tabs 649 can be bent to a horizontal position or twisted about avertical axis to secure the two sheets together. Tab 649 also may bebent down and secured to sheet 656 by adhesives, welding, brazing or thelike.

Optionally, a second sheet of material, not shown, can be attached tothe lower side of folded or corrugated sheet 641 using tabs (also notshown) which are formed out of sheet 641 during the slitting or groovingprocess. The second sheet would be secured to the bottom of foldedcorrugated sheet 641 in a manner described in connection with sheet 656.

The result is a high-strength, fatigue-resistant and lightweightcorrugated panel or deck assembly which can be used in numerousapplications.

A corrugated panel assembly similar to FIG. 17 can be constructed asshown in connection with the assembly of FIG. 18. Folded corrugatedsheet 661 includes a plurality of fold lines 662 and a plurality of tabs663. Tabs 663 are formed from sheet 661 in a manner similar to thatdescribed in connection with tab 649, only tabs 663 include fastenerreceiving openings 664. Additionally, tabs 663 are folded down to a nearhorizontal position, rather than up to a near vertical position, asdescribed in connection with tabs 649. In the horizontal position, tab663 can be used to couple a second sheet of material 666 having fastenerreceiving openings 667 therein. Sheet 666 is positioned so that opening667 align with opening 664, and fasteners are used to secure the twosheets together. As described in connection with FIG. 17, a third sheetcan be secured to the bottom of the corrugated sheet 666, although thefigure does not show the securement tabs 664 on the bottom side of thecorrugated sheet 61.

Again, by employing a plurality of grooves or slits 668 formed inaccordance with the present invention, as above described, a corrugateddeck or panel assembly can be fabricated which is very high in strength,has good fatigue resistance and is lightweight.

FIGS. 19-22 illustrate a further embodiment of a continuous corrugatedpanel or deck which can be formed using the slit sheet and method of thepresent invention. Moreover, the panel of FIGS. 19-22 illustrates thestrength advantages which can be obtained by reason of the ability tomake sharp bends or folds that have significant load carryingcapabilities. Still further, the embodiment of FIGS. 19-22 illustratesthe use of tabs to interlock a folded sheet into a high strengththree-dimensional structure.

Prior art techniques forming corrugated panels or decks often havesuffered from an inability to achieve a desired high level or percentageof chord material to the overall panel material. Generally, the purposeof the webbing is to separate the chords with the minimal web massrequired to accomplish that task. I-beams are rolled or welded formsthat use thicker top and bottom chords relative to the connecting webbetween them. The present invention enables a class of corrugatedstructures that provide for wide design flexibility in creating rigid,strong, low weight structures that can be manufactured from continuouscoils, transported in a compact coil form, and easily formed on site.The interlocking nature of this enabled embodiment avoids welding at thecorners where welding is especially subject to failure.

Sheet material 721 has been slit using the present invention and isshown in FIG. 19 in a flat state before bending or folding. As will beseen, a plurality of substantially parallel bend lines 722 have apattern of alternating arcuate slits 723 positioned on opposite sides ofthe bend lines to define obliquely extending straps skewed in oppositedirections. Slits 723 can take the form of the slits in FIG. 6 or 9, forexample. Also formed in sheet 721 are a plurality of tabs 724 whichextend outwardly of the tongue portions of slits 723, and a plurality ofkey-hole like openings 725. Openings 725 are positioned in alignedrelation to tabs 724.

In FIG. 21A tabs 724 will be seen to extend across bend line 722 fromslits 723. Tabs 724 are, therefore extensions of the tongue side ofslits 723. Key hole openings 725 is a cut-out or negative tab in thetongue side of slits 723 which have a configuration dimensioned toreceive tabs 724. In order to prevent the neck of tabs 724 from beinginterfered with by the upwardly displaced face on the opposite side ofthe slits, a notch 730 is provided in the lip side of the slits 723.Thus, the entire area of 725 and 730 is cut and falls out or is removedfrom the sheet so that tabs 724 can be inserted into notches 725/730.

In FIG. 20 the flat sheet 721 of FIG. 19 has been folded into acontinuous corrugated panel or deck 726. Panel 726 includes web portions727 and chord portions 728. As will be seen in panel 726, chords 728 arein end-to-end abutting relation over the full length of the panel onboth the upper side and the lower side of the panel to providecontinuous deck or chord surfaces. This construction affords panel 726greatly enhanced strength, for example, in bending, over panels in whichall the transverse webs are not joined by chords on both the top andbottom side of the panel. The deck or panel can be further reinforced byadding a sheet of additional material (not shown) which would furtherimprove the ratio of chord material mass to the mass of the entire deckor panel for superior strength/stiffness-to-weight ratio.

FIG. 21 illustrates in greater detail the bending or folding schemeemployed for panel 726. Commencing, for example, with end flange 729,web 727 a can be bent down and back at bend line 722 a down to a lowerside of the panel. Sheet material 721 is then bent forward at bend line722 b and chord 728 a extends in a longitudinal direction of the panelparallel to flange 729. At bend line 722 c web 727 b is bent to extendup and back to bend line 722 a, at which point chord 728 b is bentforward and extends to bend line 722 b. Web 727 is then bent back atbend line 722 d to bend line 722 c. The bending continues along thelength of panel 726 so as to produce a folded corrugated panel in whichthere are a plurality of end-to-end chords on both the top and bottom ofthe panel which are separated by connecting webs. The mass of the chordmaterial in the panel to the overall panel mass is relatively high for ahigh strength-to-weight ratio.

The ability to fold a sheet 721 in sharp or crisp folds using theslitting process of the present invention allows the apexes 731 betweenthe webs 727 and chords 728 to be relatively sharp and to be positionedin close, abutting relation. As illustrated, the panel of FIGS. 19-21has webs and chords of equal length creating equilateral triangles inwhich each apex is about 120 degrees. As will be understood, many othercorrugation geometries are equally possible.

While there are numerous ways in which folded panel 726 can be securedin a three-dimensional configuration, a preferred method is to employtabs 724 and mating keyhole openings 725 cut into sheet 721 duringformation of the bending slits.

Tabs 724 a, for example, are provided by laser or water jet cutting ofthe tabs to extend outwardly of slit tongues from flange 729 into web727 a. When web 727 a is bent downwardly and rearwardly to bend line 722b, tabs 724 a remain in the horizontal plane of flange 729. As best seenin FIG. 21A, a mating opening 725 cut into chord 728 b and aligned withtab 724 a will allow tab 724 a to be positioned in opening 725. If eachtab 724 has an enlarged head or end 734, the tabs will lock or becaptured by their mating openings 725, much as a jigsaw piece cancapture or interlock with an adjacent piece. This interlocking resistsseparation of the tabs from the mating openings in the top and bottomplanes of the panel. The tabs and openings do not need to be, andpreferably are not, dimensioned to produce an interference fit.

Interlocking of tabs 724 and openings 725 also occurs along the bottomside of panel 726, and the result is securement of the folded panel inthe form as shown in FIG. 20, even without additional securementtechniques, such as adhesives, welding, brazing or the like, whichoptionally also can be used.

In FIG. 22, the sheet slitting and bending process of FIGS. 19-21 isschematically shown as applied to the formation of a cylindrical member741. Again, webs 742 and chords 743 are formed about bend lines and thelocations of the bend lines selected so that the chords on the innerradius 744 are shorter in their length than the chords on the outerradius 746 of cylinder 741. Tabs and mating opening may be used to lockthe chords and webs in the desired configuration, depending on thethickness of the material and the radii of cylinder 741. The resultingcylindrical structure can be used, for example, as a lightweight,high-strength column or post.

In most embodiments of the present invention, and particularly those inwhich the sheet of material has a substantial thickness, commencement ofbending will automatically cause the tongue or tab portion of the slitto begin to slide in the correct direction against the face on theopposite side of the slit. When the sheet material is relatively thinand the kerf of the slit is small or zero, however the tab portions ofthe slit sheet occasionally will move in the wrong direction and therebyeffect the precision of the bend. In order to remedy this problem, it ispossible for the tongue portion of the slit to be biased in a directionproducing predictable proper bending. This solution is shown in FIGS. 23and 24A.

A sheet of material 681 is formed for bending about a plane of bend line682 using the design and sheet slitting technique of the presentinvention. Arcuate slits 683 are formed which define tongues 684 thatwill slide along opposing faces during bending of the sheet about bendline 682.

In FIG. 23 a, sheet of material 681 can be seen as it is being bent in adownward direction, as indicated by arrows 687, about bend line 682.Because tongues 684 are downwardly displaced, the lower edges or corners688 of lips 689 will tuck up and engage faces 690 of tongues in a mannerwhich will produce sliding of edges 688 along faces 690. The edges 688on each side of bend line 682 will be displaced upwardly to slide on thedownwardly pre-set tongues 684 so that bending about bend line 682predictably produces sliding of the edges along the faces of the tonguesin the desired direction during the bending process.

When sheet 681 is formed for bending using, for example, a stampingprocess in which a knife forms slit 683, the stamping die can alsoplastically deform tongues 684 in a downward direction on side of thebend line. Predictable sliding of edge 688 along face 690 in the properdirection will occur during bending so that the actual fulcrums onopposite sides of the bend line will produce precise bending along thevirtual fulcrum aligned with bend line 682. The displaced tongues alsowill cue an operator as to the proper direction for bending.

While many applications of the present invention will call for 90 degreebends, some will call for bends at other angles. The apparatus andmethod of the present invention can accommodate such bends while stillmaintaining the advantages of full edge-to-face contact. In FIG. 24, abend of about 75 degrees is illustrated.

As shown, a sheet of material 691 is formed with a slit 692 which is cutat an angle of α of about 75 degrees to the plane of sheet 691. (Acorresponding slit on the other side of bend line 693 also cut at 75degrees but skewed in the opposite direction is not shown for simplicityof illustration.) Upon bending downwardly, lower edge 694 of lip 695tucks onto and slides up face 696 of tongue 697. Once the bend reaches105 degrees, or the complimentary angle to slit angle α, the lowersurface 698 of the sheet proximate edge 694 will be coplanar with andevenly supported on face 696 of the tongue.

Today most commercial laser cutters with power capable of cutting bothplastics and metals are sheet fed. There is, however, supply-roll fedlaser cutting equipment commercially available, but such equipment thatexists today does not roll the cut material back into a coil. Thus,reel-to-reel laser cutting equipment is not in use or commerciallyavailable.

The advantage of roll fed cutting combined with a coil mechanism, in thecontext of the present invention, is that very large or very complex,information-rich structures can be designed in CAD, cut, and then thesepre-engineered structures can be recoiled into a compact form. Once inthe coiled, compact form, they may be transported more conveniently, forexample, on a flat-bed truck or rail car or launched into outer space.Upon arrival at the location of use, the material is uncoiled and bentor folded along the bend lines dictated and structurally supported bythe arcuate slits and oblique straps cut into the metallic or plasticsheet.

The sheet slitting or grooving apparatus and method of the presentinvention can be incorporated into a reel-to-reel process in at leastthree ways. Widely available throughout industry are flat-bed lasercutters of many types. The first approach uses a coil on one end of aflat-bed laser cutter, the laser cutter in the middle and a winding rollfor reforming a coil of partially cut material. The material is advancedthrough the system by hand and pin or edge-notch registration featuresare cut into the flattened sheet. The sheet is aligned in both X and Yaxis by physically docking the cut features with a jig attached to thelaser cutter bed. In this way, piece-wise advancement can occurincluding the alignment of slit-assisted bending features of the presentinvention. The novelty is in the combination of the registration systemwith the uncoiling and coiling of material-together with the applicationof cut bend-producing features of the present invention that enablelow-force, precisely located, high strength bent or folded structures.

A second approach is to advance a coil through a laser cutter using thewell-known technique of a power unwind, stop, cut and power rewind.

A third approach is shown in FIG. 25. It employs a smooth, continuousweb transport, with both unwind and rewind. Sheet material 701 isunwound from supply coil 702, and the motion and/or optics of the CNCcutter 703 is controlled to compensate for the rolling frame of material701. CNC cutter 703 can be a laser cutter or a water jet cutter formedand controlled to cut the desired slit patterns into sheet 701. Aftercutting, sheet 701 is wound onto coil 704.

Since coiled sheet stock often will have a coil-set curl, the use of aleveling step or leveling apparatus 706 after unwinding coil 702 is anoption. Sheet stock 701 can be driven through the processing line bypinch rollers 707 and drive motors at coils 702 and 704 and additionallyat roller 710.

One reason that reel-to-reel processing has not been previously used isthat the edges or contours of the cut-out features tend to interlock andsnag as successive layers are would up on coil 704, particularly whenthe low-force slit-assisted bend features of the present inventionenable a foldable tab or flap. The very act of recoiling material 701will tend to make the cut tabs or flaps extend tangentially to thewinding coil. Two methods can be used to address this issue. One is theuse of thin, easily removed hang-tabs in combination with rewinding acoil of metal and other rigid materials that have these low-forcefolding features of the present invention that tend to extend from therewound coil tangentially. A second method is shown in FIG. 25, namely,to co-wind a polymer web 708 onto coil 704. Web 708 should be tough andnot easily punctured, yet thin in gage. Polypropylene and polyethyleneare but two useful examples.

One technique for increasing the throughput of reel-to-reel processingsystems is the use of laser cutter 703 having multiple laser beams forcutting the slit-assisted, low-force bend features of the presentinvention. Foldable box beams, such as is shown in FIG. 12, need severalbend-assisting arcuate slits that are arranged parallel to the coil'swinding direction, about a desired bend line. Multiple fiber lasers, forexample, that are linked together mechanically and whose motioncontroller is a single, joined, mechanical system, with a single motioncontroller, can produce all of the parallel bends at the same time,while other lasers with independent motion actuation systems and motioncontrollers can produce all other cut features, such as the notchededges.

The methods and apparatus of the three reel-to-reel processing systemsdescribed above, combined with the low bending-force, high strength bendfeatures of the present invention, enable a class of products, frombeams, to ladders, to building stud and joist systems, to be formed,coiled, subsequently uncoiled and folded into deterministic dimensionsof impressive structural integrity, when and where they are needed aftercompact storage or transport in coiled form. This technique hasapplications in space, in the military, in commercial and residentialconstruction and many other industries where the costs and effort ofgetting materials to a site are prohibitively expensive and difficultwhen parts are already in an assembled state.

Optionally the reel-to-reel processing line of FIG. 25 can also includea pair of hard-tooled die cutters 709. Using male and female stampingshapes to stamp out the arcuate slits and drop-out features, the diecutters also can be plates and apply incremental material handlingtechniques, but most preferably, they are hard tooled rotary dies 709.

The advantage of the CNC cutting approach to fabricating coil-woundengineered folding structures is that non-repetitive features are easilyprogrammed into the cutting process. The advantage of the hard tooledstamping or rotary die cutting approach, whether intermittent orcontinuous, is that repetitive features, especially the arcuate slits,can be efficiently made.

The greatest benefits of maximum throughput and flexibility may beadvisable using CNC cutting in combination with the hard-tooledstamping/die cutting to yield an inline system with both forming stepslocated between the unwinding and rewinding steps of the process. In thecombined system, such as shown in FIG. 25, each forming tool operates toits own advantage.

FIG. 25 illustrates a method can be used to form three-dimensionalstructures for use particularly at locations remote of the location atwhich the structure is slit and/or partially assembled prior to bending.One application is of particular interest is the fabrication ofthree-dimensional structures in outer space. Currently such structuresare assembled in outer space from three-dimensional modules; theygenerally are not actually fabricated in outer space. The problem withspace assembly is that the modules require an undesirable amount ofvolume in the payload of orbital space vehicles. Heretofore, one problemwith fabrication in outer space has been that the tools required to formhigh-strength, three-dimensional structures have been prohibitivelylarge and bulky. Another problem with assembly in space can beassociated with a high part count and high fastener count. On the onehand, bulky near complete modules have been launched and fastenedtogether. On the other hand, heretofore, dense packing of unassembledmodules has resulted in a high part count and high fastener count.

In FIG. 26, a coil 339 of sheet material 341 is shown which has beendesigned and provided with slits or grooved on two bend lines 345. Sheet341 is also formed with openings 346 and tabs 348 periodicallypositioned proximate opposed sheet edges. As will be seen, slits 343 mayadvantageously take the configuration as shown in FIG. 6. As will beappreciated, coil 339 is a highly compact configuration for thetransport of sheet material. Sheet 341 can be formed with slits 243,openings 346 and tabs 348, as well as other desired structural features,at an earth-bound shop having unlimited fabrication equipment, forexample, using the reel-to-reel processing line of FIG. 25. The coiledsheet is next transported by a space vehicle to an outer space location.Sheet 341 can then be unrolled from coil 339, and either, while beingunrolled, or thereafter, the sheet can be fabricated, using hand toolsor moderately powered tools, into a three-dimensional structure. Suchfabrication is accomplished by bending the sheet along bend lines 345and by bending tabs 348 into openings 346 so as to lock the sheet in athree-dimensional structure such as a triangular beam 350, as shown atthe right-hand side of FIG. 26.

As shown in FIG. 26, structure 350 is an elongated beam with atriangular cross section can, in turn, be coupled to other structures toproduce complex three-dimensional space structures and habitats. Whenthe sheet bending slit configuration of the present invention isemployed, each of the bends produced at the pattern of slits 343 willpreferably include the edge-to-face support of the sheet material whichwill make the bends capable of withstanding substantial loading.Obviously, other beam and structural configurations, such as the boxbeam of FIGS. 13 and 14, the deck of FIG. 20 or the column of FIG. 22,can be produced by folding along bend lines having slits of the typedescribed above.

Moreover, using the slitting and grooving method and apparatus of thepresent invention ensures the precise positioning of the opposed edgesof the sheet 341 and openings 346 and tabs 348 so as to enable closureof structure 350. If the structure to be formed needs to be fluid-tightand slitting is employed, the bends produced by slits 343 can beadhesively or otherwise filled, for example, by welding or brazing. Itis also possible to provide numerous other closure configurations orfastening schemes, including welding along the abutting edges of sheet341 and overlapping of an edge of the sheet with a side wall and the useof tabs and/or fasteners.

Another form of box beam which illustrates the flexibility of theapparatus and process of the present invention is shown in FIGS.27A-27G, namely a cross or self-braced box beam.

Sheet of material 801 is shown in FIG. 27A as being slit along bendlines 802 and 803. Additionally, a plurality of transverse slits 804 areprovided which will be used to provide beam cross-bracing sheet portions806. Bending of sheet 801 into a cross-braced box beam 807 (FIG. 27G) isshown in the sequence of FIGS. 27B-27G.

First, the side of the sheet having the cross-bracing sheet portions 806can be bent to the position of FIG. 27B. Next, the sheet is bent alongbend lines 803 to produce the cross braces 806 of FIG. 27C. Sheet 801 isthen bent about bend line 802 a to the position of FIG. 27D. The sheetis bent about bend lines 802 b and 802 c in FIGS. 27E and 27F, andfinally side flange 805 is bent up and the sheet bent about bend line802 d to produce beam 807 of FIG. 27G. Fasteners can be placed inopenings 808 and 809 (which are formed in aligned registered relation insheet 801), such as rivets or screws, can be used to secure side flange805 to the remainder of the box beam to produce a structure which willnot bend or unfold. Beam 807 will be seen to trap or capture at itscenter an X-shaped cross-beam array extending along the beam to give itsubstantially enhanced strength. An extremely high-strength to weight,internally braced box beam, therefore, can be designed and formed from asingle sheet of material using the process of the present invention.

As an optional step that can be added to many different structuresformed using the apparatus and method of the present invention,protective corners or shin guards 810 (FIG. 27G) can be attached overbent corners 802 to effect a smooth and/or decorative corner treatment.Thus, L-shaped shin guard 810 can be added to beam 807, as indicated byarrows 820, and secured in place by, for example, adhesives orfasteners. Shin guards 810 can be metallic plastic or even reflective toproduce decorative effects, as well as to provide impact protection, tosmooth and/or to seal or pot the corner bends. Shin guard 810 could evenencircle the beam or other three-dimensional structure. Attached shinguards can assist in load transfer across the bends.

In the cross braced box beam 807 of FIGS. 27A-27G, the cross bracingsheet portions 806 are bent to an “X” configuration and then captured ortrapped within the folded beam to provide internal bracing. Anotherapproach to the bracing of structures having adjacent walls in differentplanes is to employ swing-out sheet portions.

FIGS. 34A-34E illustrate the use of swing-out bracing in another boxbeam that also has a pattern of weight-saving cutouts. In FIG. 34A,sheet 811 has been slit using the present invention with a plurality ofbend lines 812. Sheet 811 has further been cut or stamped with cutoutsor weight saving openings 813. Additionally, in order to provide bracingof the folded walls of the beam, a plurality of swing-out sheet portions814 have been provided which can be bent around bend lines 815.

In FIG. 34B swing-outs 814 have been folded or swung out of the plane ofsheet 811 around bend lines 815, while in FIG. 34C, the outside edges816 of the sheet have been bent to a vertical orientation around bendlines 812. In FIG. 34D one side wall portion 817 of sheet 811 has beenbent again around a bend 812, and in FIG. 34E the other side wallportion 817 has been bent around another bend line 812 to complete thebox beam 818.

The last bending step, namely, bending from the configuration of FIG.34D to that of 34E, causes edge portions 816 to overlap and causesswing-outs 814 to overlap. Both edges 816 and swing-out 814 can beprovided with fastener-receiving openings 819 which will become alignedor superimposed as the beam is folded to the FIG. 34E condition byreason of the high precision or accuracy possible when employing theedge-to-face bending technique of the present invention. Thus,fasteners, such as rivets or screws, not shown, can be inserted intoopening 819 to secure edges 816 together against unfolding of beam 819,and to secure swing-outs 814 together to provide bracing betweenmutually perpendicular walls of the beam, as well as bracing across thebeam. As will be apparent, the number of bracing swing-outs can beincreased from that shown in the illustrated embodiment, and the use ofswing-outs to brace adjacent walls in different planes has applicationto many structures other than box-beams.

Turning now to FIGS. 29 and 30, the advantages of low-force sheetbending enabled by the present invention can be illustrated. In FIG. 29,a sheet of material 841 is shown which has a plurality of arcuate slits842 formed along bend lines in a manner above described. Formation ofbox 843 from sheet 841 can be easily accomplished using low-forcetechniques.

Sheet 843 can be placed over opening 844 in die 846 and the four sides847 of the box simultaneously bent to upright positions. An actuatordriven plunger 848 can be employed or a vacuum source coupled to apply avacuum to die 846 through conduit 849 used. Little or no clamping ofsheet 841 to die 846 is required; only positioning of sheet 841 so thatthe bend lines are in mating relationship with opening 844 in the die.This can be accomplished, for example, by providing indexing pins (notshown) on the top surface of the die proximate the corners of opening844. The indexing pins would engage sheet 844 at the apexes betweensides 847 of sheet 841.

Depending upon the material being bent and its thickness, a negativepressure at conduit 849 will be sufficient to pull sheet 841 down intothe die and thereby bend sides 847 up, or for thicker sheets andstronger materials, plunger 848 may also be used or required to effectbending.

Box 843 can be used, for example, as RFI shields for small circuitboards, such as the ones commonly found in hand-held cell phones, havebeen made by the prior art technique of progressive die stamping. Theadvantage of progressive die stamping is that sufficient precision canbe achieved and it is suitable to low cost, mass production. However,with the rapid change in products that face this market, new shielddesigns require that the hard tooling be frequently replaced. This isespecially problematic at the development end of the product life cyclewhere many changes occur before the final design is chosen. Anotherdifficulty with relying on hard tooling is that the ramp-up to fullproduction must wait until the hard tooling is available. This can be asmuch as eight weeks, which is very expensive in a market with rapiddesign changes and short product life. Yet another problem with theprogressive die stamping has to do with accessibility to the underlyingcomponents for diagnostics or repair. If a significant fraction of achip batch is faulty and may need repair, a two-piece RFI shield unit isemployed with a low profile fence, soldered to the circuit and a “shoebox lid” covering it with an interference fit. This disadvantage is thatthe fence below take some horizontal “real estate” away from the circuitboard and two pieces are always more expensive to manufacture than one.Another prior art solution to accessibility is the method of using a rowof circular perforations in the shield lid that can be severed to allowan area of the lid to be hinged upward along one side. This perforateddoor approach crates the possibility of some RFI leakage and it isdifficult to cut and reseal the lid.

Box 843 of FIG. 29 shows a solution to the aforementioned problems usingthe techniques of the present invention. The RFI shields manufacturedusing arcuate slit assisted bending methods can be rapidly prototypedwithout hard tooling using a CAD system for design and a CNC cuttingprocess such as a laser cutter. Folding to the required shape can bereadily accomplished by hand tools or the fabrication equipment of FIG.29.

The ramp-up to full production can be accomplished immediately by lasercutting the initial production volumes required to enter the marker.Lower cost stamping tools to stamp out the biased tongue-tabs needed forthe geometry disclosed can be fabricated during the ramp-up phase thatinitially is supplied by a CNC cut solution. In this way, the cost ofdesign, ramp-up, and production can be lowered relative to the currentpractice of waiting for progressive cavity dies to be manufactured.

Another advantage of the present invention is the built-in access doorfor servicing the parts within. By severing the straps defined by slits842 around three sides of shield 843, and having previously solderededges 850 of the low profile rectangular box 843 to the circuit board,the panel 840 of box 843 can be hinged 90 degrees to allow for temporaryservice access. When repairs are complete, the lid or panel 840 can beclosed again and re-soldered at the corners. Most metal alloys suitablefor RFI shielding will allow for eight or more accesses in this mannerbefore the hinged straps fail.

In FIG. 30 a series of steps is shown in which a sheet 861, which hasbeen slit according to the present invention, can be popped up into abox using a pneumatic bladder or vacuum grippers.

Sheet 861 is shown in a flat form at the left side of the sequence ofFIG. 30. Sheet 861 is, in fact, two identical sheets which have beencoupled together at bend lines 826 at the outer edges of sides 863 ofthe sheets, as will become apparent as the box is formed. Sheet 861 canbe transported in the substantially flat state shown on the left end ofthe sequence and then, at the use site, popped up to thethree-dimensional box 865 shown at the right hand side of the sequence.This in-the-field formation of box 865 can be easily accomplished usingpneumatics or hydraulics because the bending of sheet 861 requires onlythe minimal force necessary to bend the oblique bending straps.

One bending technique would be to employ suction or vacuum grippers 864which are moved, as indicated by arrows 866, down into contact with aplanar central sheet portion 867 of sheet 861. A vacuum is applied tosuction grippers 864 and then the grippers are moved apart, as indicatedby arrows 868 until box 865 is fully distended, as shown at the righthand side of FIG. 30.

Another approach is to insert an expansible bladder 869 into theslightly distended box, as shown by arrow 871. Such insertion can beaccomplished before transportation or in the field. Bladder 869 is theninflated pneumatically or hydraulically and the box gradually distendedor bent up to the condition shown at the right hand side of FIG. 30.

Box 865 can be secured in the configuration shown at the right hand sideof FIG. 30 by, for example, welding, brazing or adhesively securing sidepanels 863 at corners 872.

A further advantage of the high precision bending or folding process ofthe present invention is that geometric information may be embedded inthe planar material at the same time that the low-force, high precisionbending structures are fabricated. This information may be accuratelyand predictably communicated into an anticipated 3D spatial relationshipat very low cost.

In the past, symbols and geometric conventions have been used to conveyinformation about the assembly of structures. One aspect of the presentinvention is that the bending or folding instructions may be imparted tothe flat parts of the sheet material at the same time that they areformed with bending slits or grooves. Alternatively, foldinginstructions may be imparted to the flat parts through a secondaryprocess such as printing, labeling, or tagging. Additionally,information may be embedded in the flat form that is intended toinstruct the assembly process of similarly precision-bent structures orthe adjoining of parts from non-folded prior art and future artfabrication methods.

For example, a continuous pre-engineered wall structured may be formedfrom a single sheet of material that is folded into top and bottomjoists with folded-up studs. All anticipated windows, doors andelectrical boxes can be embedded as physical geometric information inthe flat part for subsequent folding and assembly into the building. Aconvention may be established that a round hole in the structure isindicative of electrical conduit that will later be threaded through thehole. A round-cornered square hole may be indicative of hot water copperpipe that should be passed through the wall. In this way, the feature isnot only located in the flat part, but it is very accurately translatedinto correct 3D relationship, and finally, such conventions communicateto trades people, who are not involved with the structural erection ofthe building, where their activities intersect with the structure.Moreover, communication of such information anticipates the tradespeople's activity so that they do not have to modify and repair thestructure as they thread their infrastructure through the building.

FIGS. 32A-32E illustrate an embodiment of a stud wall which can befolded out of a single sheet of material using the sheet bending methodof the present invention. In FIGS. 32A-32E no attempt has been made toillustrate openings or the like which are precisely positioned andshaped to communicate information, but such data can be preciselylocated during the sheet slitting process. It should also be noted thatthe folded sheet of FIG. 32E can either be a stud wall with studs joinedto joists or a ladder with rungs joined to side rails

Turning to FIG. 32A, sheet of material 901 has been slit along aplurality of bend lines to enable formation of a stud wall or ladderstructure. The slits are formed and positioned as taught herein.

In FIG. 32B the side wall portions 902 of eventual studs or ladder rung903 have been folded up along bend lines 904 from flat sheet 901. Thenext step is to fold up an additional end wall or step portion 906 alongbend line 907, as shown in FIG. 32C. In FIG. 32D the joists or ladderrails 908 are folded up along bend line 909, and finally thejoists/rails 908 are folded again along bend line 911 in FIG. 32E. Thislast fold causes openings 912 in joist/rails 908 to be superimposed inaligned or registered relation to openings 913 (FIG. 32D) in side walls902 of the studs/rungs 903. Fasteners, such as rivets or screws can beused to secure the joist/rails 908 to the studshungs 903 and therebysecure the assembly in a load bearing three-dimensional form 914.

When used as a ladder, rails 908 are vertically extending while rungs903 are horizontal. When used as a stud wall, joists 908 are horizontaland studs 903 are vertically extending. As will be appreciated, therungs/studs and rails/joists also would be scaled appropriately to theapplication.

As set forth above, most uses of the slitting process and slit sheets ofthe present invention will require that a plurality of slits be placedin offset relation along opposite sides of the desired bend line. Thisapproach will produce the most accurate or precise sheet stock bendssince three will be two opposed and spaced apart actual fulcrums thatprecisely cause the position of the virtual fulcrum to be between theactual fulcrums on the desired bend line.

While there is a very minor loss of bending precision, the technique ofthe present invention can also be employed using a single slit andbending straps configured to produce bending of the sheet of materialalong a bend line, while edge-to-face engagement of the sheet portionsacross the slit occurs. This single slit bending is illustrated in FIGS.35 and 36.

In FIG. 35 a sheet of material 941 is shown which has been slit forbending into a wheel roller housing, generally designated 942, as shownin FIG. 36. Sheet 941 includes a slit 943 for bending of ear 944 aboutbend line 946. As will be seen, there is no slit on the side of bendline 946 opposed to slit 943. Nevertheless, ear 944 includes twoshoulders 947 that define bending straps 948 with arcuate end portion949 of slit 943. It also will be apparent that the central axes 951 ofbending straps 948 are oblique to bending line 946 in oppositely skeweddirections.

When ear 944 is bent into the page for FIG. 35, oblique straps 948 willbend and twist and at the same time pull or draw lip 952 on the ear sideof slit 943 up into engagement with the face of tongue 953 on the bodyside of the slit. Thus, sliding edge-to-face engagement again isproduced by reason of oblique bending straps 948, correctly scaled andshaped.

Sheet 941 has other examples of arcuate bending slits which combine withpartial opposed sits or edges of the sheet to provide bending strapsthat will produce edge-to-face bending. For bending line 956, forexample, slit 943 a is opposed at one end by a partial slit 957 havingan arcuate end 958 that combines with arcuate end 949 a to define anoblique bending strap 948 a. At the opposite end of slit 943 a anarcuate edge portion 959 combines with arcuate slit end 949 a to defineanother oppositely skewed strap 948 a.

The result of the configuration of straps 948 a is edge-to-face bendingabout bend line 956.

Slit 943 b is formed as a mirror image of slit 943 a with an arcuateedge and partial slit cooperating to define oblique bending straps 948b. Similarly, slit 943 c cooperates with an edge and partial slit todefine oblique bending straps 948 c that ensure edge-to-face bending.Finally, slit 943 d cooperated with slit portions 960 to defineobliquely oriented bending straps 948 d.

The single slit embodiment of the present apparatus and method asillustrated in FIG. 35 is somewhat less precise in the positioning ofthe bend on desired bending line, but the loss of accuracy is notsignificant for many applications. In the structure illustrated in FIG.36, an axle 961 for roller 962 passes through openings 963, 964 and 965(FIG. 35) which must come into alignment when sheet 941 is bent into thethree-dimensional housing 942 of FIG. 36. The single slit embodiment,therefore, will produce bends which are still sufficiently precise as toenable alignment of openings 963, 964 and 965 to within a fewthousandths of an inch for insertion of axle 961 therethrough.

In FIG. 37, bend line termination or edge-effects related to theslitting process and apparatus of the present invention are illustrated.A sheet of material 971 is shown with five bend lines 972-976. Slits 981are formed in the sheet along the bend lines as described above. Theedge 982 of sheet 971 should be considered when designing the slitlayout because it can influence the positioning of the slits.

On bend line 972 slits 981 were given a length and spacing such that apartial slit 981 a opens to edge 982 of the sheet of material. This isan acceptable bend line termination strategy. On bend line 973, partialslit 981 b again opens to edge 982, but the partial slit 981 b is longenough to include arcuate end 983 so that a bending strap 984 is presentto oppose bending strap 986. Slit 987 can also be seen to have arectangular opening 988 extending across the slit. Opening 988 is in thecentral portion of slit 987 and therefore will not significantlyinfluence bending straps 984 or 986, nor will it effect edge-to-facebending.

On bend line 974, slit 981 c has an arcuate end 989 which defines withsloping edge portion 991 an oblique bending strap 992. A similargeometry is shown for slit 981 d and edge portion 993. The use of anedge of a sheet to partially define a bending strap is also employed inconnection with the slits of FIG. 35, as above described.

Finally, on bend line 976 arcuate edge portion 994 cooperates witharcuate end 996 of slit 981 e to define strap 997. Thus, the edgeportion 994 requires a slit layout which inverts slit 981 e from theorientation of slit 981 d and illustrates that the finite nature of theslits requires that edge effects be considered when laying out theslits. In most cases, slit length can be slightly adjusted to producethe desired bend line termination or edge effect.

In a further aspect of the present invention, as schematically shown inFIG. 31, a method is provided for forming three-dimensional structures.The first step is designing the three-dimensional structure. Thisinvolves an initial sub-step 370 a of imagining the design. Onceconceptualized, designing will often, but not necessarily, proceed witha step 370 b or 370 c in which CAD or computer implemented designingtakes place. The step 371 of selecting a sheet of material and itsthickness optionally can occur before or during CAD design steps 370 bor 370 c.

As can be seen in FIG. 31, CAD design steps 370 b and 370 c can includevarious alternative sub-steps. Thus, a common approach is sub-step 370 b₁ in which the conceptual design is built in 3-D CAD and then flattened.Alternatively at step 370 b ₂, the design can be built up bysuccessively bending sheet flanges or portions. One can also design in2-D and declare or locate the bend lines, which is sub-step 370 b ₃.Placement of the proper or best-designed slits or grooves of the presentinvention can be done through software, at step 370 b ₄ or manually atthe step 370 b ₅.

The design process of the present invention can also be based upon aselection, usually by computer or a CAD software program, at sub-step370 c ₁ among a plurality of stored designs and/or parts. The CAD systemcan then, at sub-step 370 c ₂, modify the selected part to achieve thenew or desired design, if modification is required. Finally, at sub-step370 c ₃ the part is unfolded by the software into a flat state.

Once designed, the next step is a slitting or grooving step 373,preferably by employing a CNC controller to drive a sheet stock slittingapparatus. Thus, at sub-step 373 a data, representing the flat part andthe designed slits or grooves, are transferred from the CAD or CAMsystems to a CNC controller. The controller then controls slitting andother formation steps for the cutting and fabricating equipment. Atsub-step 373 b, therefore, the flat part is formed using additive(molding, casting, stereo lithography) or subtractive (slitting,cutting) or severing (punching, stamping, die cutting) fabricationtechnique.

Optionally, the formed flat sheet can also undergo such steps as surfacetreatment 373 c, affixation of components 373 d, testing 373 e ₄ andstorage 373 f, usually in a flat or coiled condition.

Often a transportation step 375 will occur before the sheet material isbent or folded at step 377. The slit sheet stock is most efficientlytransported from the fabrication site to a remote bending and assemblysite in a flat or coiled condition.

Bending or folding 377 is precise and low-force. For most structuresbending occurs along a plurality of bend lines and often continues untiltwo portions of the sheet are abutting, at which point they can becoupled together at the abutting portions of the sheet to produce arigid load-bearing three-dimensional structure at step 379. Optionally,the structure can be secured in a three-dimensional, load bearingconfiguration by an enveloping step, which couples the folded parttogether by encircling it.

Envelopment can be used for at least three strategies. In the presentinvention, the angle of a fold is not informed by the geometry of slitsthat form it. (Notwithstanding the technique of using a slit tilt angleto affect maximum contact area of edge to face engagement for aparticular angle of folding, as shown in FIG. 24.) The angle of eachfold is generally dictated by at least three interlocking planes. Insome cases there is no opportunity to interlock three orthogonallyindependent planes, so an alternate method of defining a restrictedrotational angle is needed. One method is to fold the structure againsta reference structure of known angular relationship and lock theangle(s) into place by methods of adhesive(s), brazing, welding,soldering, or attaching structural shin guards to the inside or outsideof the fold. Another method is to use an interior structure of definedangular form and bend the structure around it, that is to envelop theinterior structure. This second method is referred to in the design andfabrication process diagram of FIG. 31, by reference numeral 376 a-b. Inthis embodiment of envelopment, the interior part may be left in place(376 b) or in some cases, it aids in the folding process only and issubsequently removed (376 a).

Another use for envelopment is to capture, which is the process ofdocking together a folded sheet structure of the present invention witha functional part that may or may not be formed by the presentinvention, by enfolding or enveloping parts or modules within anotherstructure. For example, FIG. 16 illustrates but one of many “capture”opportunities of the enabling feature of envelopment in the presentinvention 376 b. Thus, column 631 is enveloped by folded sheet 611.

Yet another class of envelopment can occur, when connections are madebetween two or more modules of folded plate construction of the presentinvention, or between two or more components that include at least onestructure of folded plate construction of the present invention. Thethree-dimensional positional accuracy of features formed in a planarmaterial of the present invention, combined with the enveloping natureof the closure or coupling process, enable a method of joining togethermultiple pieces with a very high rate of success that does not requiresecondary cut and fit adjustments. This is distinct from the capacity ofthe present invention to align fastening features, such as holes, tabsand slots. It is a method of joining together by wrapping around.

The process of the present invention can also include an iterative step380. The ability to create low-cost three-dimensional parts using thepresent method affords the designer the practical luxury of being ableto tweak the design before settling on a production design.

The slit-base bending method and apparatus of the present invention arecapable of highly precise bending tolerances. The original slits can belaid out with extreme precision using a CNC machine to control, forexample, a laser, or water jet cutter, stamping or punching die, and thebends which are produced will be located with ±0.005 inches tolerancewhile working with macroscopic parts. This is at least as good or betterthan can be achieved using a press brake and a highly skilled operator.One additional advantage of using a stamping die is that the die can bewedge-shaped to compress the slit transversely or in the kerf widthdirection. This will compress the sheet material locally at the slit forbetter fatigue resistance. Such transverse compression also must beconsidered when designing a kerf width to produce edge-to-face contactduring bending. It also is possible to follow laser or water jet cuttingby a transverse compression of the slit with a wedge shaped stamping dieto enhance fatigue resistance.

Moreover, when using the bending scheme of the present invention, thetolerances errors do not accumulate, as would be the case for a pressbrake. Alternatively, the slits or grooves can be cast or molded into asheet of material or cast three-dimensional member having a sheet-likeextension or flap that needed to be folded.

While working with materials of near microscopic or microscopicdimensions, other forming methods commonly used in the field ofmicroelectronics and MEMS such a e-beam lithography and etching may beused to effect the required geometry of the present invention withextreme accuracy.

Rather than manipulating a laser beam (or sheet of material) to producecurved grooves or slits, such beams can also be optionally controlled orshaped to the desired configuration and used to cut grooves or slitswithout beam movement. The power requirements presently make this mostfeasible for light gauge sheets of metals or plastics.

Fabrication techniques in the method of the present invention also mayinclude steps such as deburring the slits or grooves, solvent etching,anodizing, treating to prevent surface corrosion, and applying compliantcoatings, such as paints, polymers, and various caulking compounds.

From the above description it also will be understood that anotheraspect of the method for precision bending of a sheet material of thepresent invention includes the step of forming a plurality oflongitudinally extending slits or grooves in axially spaced relation ina direction extending along and proximate a bend line to define bendingstrap webs between pairs of longitudinally adjacent slits. In oneembodiment, the longitudinally extending slits are each formed bylongitudinally extending slit segments that are connected by at leastone transversely extending slit segment. In a second embodiment, theslits or grooves are arcs or have end portions which diverge away fromthe bend line to define bending straps, which are preferably oblique tothe bend line and increasing in width. In both embodiments, the strapscan produce bending about virtual fulcrums with resulting edge-to-faceengagement of the sheet material on opposite sides of the slits. Thenumber and length of the bending straps webs and slits or grooves alsocan be varied considerably within the scope of the present invention.The width or cross-sectional area of the bending straps and thetransverse divergence of the straps also can be varied independently ofthe transverse spacing between slits. An additional step of the presentmethod is bending of the sheet of material substantially along the bendline across the bending web.

The method of the present invention can be applied to various types ofsheet stock. It is particularly well suited for use with metal sheetstock, such as aluminum or steel, which can have substantial thicknessand a variety of tempers (for example, 2 inch carbon steel, 6061aluminum with a T6 temper, some ceramics and composites). Certain typesof plastic or polymer sheets and plastically deformable compositesheets, however, also may be suitable for bending using the method ofthe present invention. The properties of these materials are relative toa given temperature and fluctuations in temperature may be required tomake a particular material suitable in the context of the presentinvention. The present method and resulting sheets of slit material areparticularly well suited for precision bending at locations remote ofthe slitter or groover. Moreover, the bends may be produced preciselywithout using a press brake.

Sheet stock can also be press brake bent, as well as slit or grooved,for later bending by the fabricator. This allows the sheet stock to beshipped in a flat or nested configuration for bending at a remotemanufacturing site to complete the enclosure. Press brake bends can bestronger than unreinforced slit bends so that a combination of the twocan be used to enhance the strength of the resulting product, with thepress brake bends being positioned, for example, along the sheet edges.The slit or grooved bends can only be partially bent to open outwardlyslightly so that such sheets can still be nested for shipping.

The bent product has overlapping edge-to-face engagement and support.This enhances the ability of the product to withstand loading fromvarious directions without significant stressing of the bending straps.If further strength is required, or for cosmetic reasons, the bent sheetmaterial can also be reinforced, for example by welding or otherwiseattaching a shin guard or bent sheet along the bend line. It should benoted that one of the advantages of forming slits with essentially zerokerf, is that the bent sheet has fewer openings therethrough along thebend line. Thus, welding or filling along the bend line for cosmeticreasons is less likely to be required.

It will be noted that while straight line bends have thus far beenillustrated, arcuate bends can also be achieved. One technique forproducing curved bend lines is shown in FIG. 33, namely, to layoutidentical strap-defining structures along a curved bend line so thevirtual fulcrums fall on the desired curved centerline.

Sheet 931 has been slit with identical slits 932 which are positioned onopposite sides of curved bend lines 933 and folded into a corrugatedpanel. Slits 932 are shown as having a form similar to the sits of FIG.6 with a central portion that is linear and diverging or curving awayend portions. Slits 932, however, are laid out bend lines. As radius ofcurvature of bend lines 933 decreases, the length of slits 932 alongbend lines 932 can be shortened to better approximate the curve.

It should be noted that the corrugated sheet 931 has a hat-shaped crosssection which is often found in roll formed corrugated panels. When usedas a decking structure, this construction is not as desirable as thecontinuous panel of FIG. 20, because chord sheet portions 934 onlycomprise about one-half the overall panel mass, but in otherapplications it has advantages and requires less material.

A second technique is to use non-identical strap-defining slits to shapethe bending straps to produce a smooth curved bend. The bent sheet willhave curved surfaces on both sides of the bend line. If stepped slitsare used, the longitudinally extending slit segments can be shortened.

FIGS. 38A-FIG. 38C illustrate another embodiment of a chassis, with FIG.38B and FIG. 38C being schematic in that details shown in FIG. 38A areomitted for clarity. In this embodiment, sheet 1380 is shaped to form athree-dimensional object having structural leg or frame members. As canbe seen in FIG. 38B, the resulting three-dimensional object havingsubstantially open sides which may facilitate access to components thatare supported on or within the chassis, and which open sides may alsoreduce material necessary to produce a given three-dimensional item.

The peripheral shape of sheet 1380 may be formed by any suitable meansincluding punching, stamping, roll-forming, machining, laser cutting,water jet cutting, and the like. Furthermore, sheet 1380 is also formedwith conventional surface features including conventional stampedfeatures such as stamped zones 1383. Stamped zones 1383 provideclearance means for various components to be positioned within or on thechassis in a well known manner. In particular, the stamped zones may beformed and dimensioned to accommodate the geometry of articles to beaffixed to the chassis. For example, a component may be located within aparticular stamped zone by a fastener which extends through an aperturelocated within the stamped zone or other suitable means. As FIG. 38Ashows, embodiments of the chassis include stamped zones 1383. Indifferent embodiments, the stamped zones may be cosmetic, or formed anddimensioned to stiffen or otherwise modify the structural properties ofthe chassis, including the attachment tabs. Many variations can be usedin accordance with the present invention.

Both FIG. 38A and FIG. 38B show sheet 1380 to include attachment tabs1381 and fastener-receiving openings 1382 on the tabs and on portions ofthe sheet adjacent the tabs. Respective openings may be aligned with oneanother and fitted with fasteners to secure the assembly in a loadbearing three-dimensional form.

Sheet 1380 also includes bending strap-defining structures 1384 whichform precision bend lines 1385. FIG. 38A shows the sheet after formationof the bending strap-defining structures and stamped zones. FIG. 38B, bycomparison, shows the three-dimensional chassis after complete bendingalong the bend lines. FIG. 38C shows several chassis in an incomplete,intermediate form in which chassis lay one within another to form astack for shipping purposes.

In FIG. 38A, sheet 380 is flat. To form a three-dimensional structurefrom the two-dimensional (or more precisely quasi two-dimensional)sheet, one bends the sheet along bend lines 1385. After full bending,the chassis has a stepped, or zigzag, configuration, as FIG. 38B shows.Moreover, as shown, at least some of the attachment tabs interleave withother adjacent attachment tabs such that correspondingfastener-receiving openings 1381 align. With fasteners (not shown)placed in the fastener-receiving openings, the chassis forms a rigidthree-dimensional support frame. In different embodiments, the chassismay be attached to external elements (for example by attachment tabs, asin FIG. 38B and/or other components may be affixed to the chassis.

FIG. 38C shows several sheets 1380 in an incomplete, transitionary formbetween a flat sheet, as in FIG. 38A, and a fully formed article, as inFIG. 38B. In the transitionary, or intermediate, form, the sheet hasbeen only partially bent. Such incomplete formation is advantageousbecause, when partially bent, chassis engage one into another to form astable stack. Stackability is very advantageous with respect to storageor shipping. Full formation, as in FIG. 38B, may be accomplishedeventually by further bending of the sheet.

In another embodiment of the present invention shown in FIG. 39A andFIG. 39B, respectively, a sheet of material may be configured to becomea three-dimensional curved channel. Both figures show sheet 1390 havinga sheet periphery 1391, flange 1392, bend curve 1393, bendingstrap-defining structures 1394 and channel profile 1395. FIG. 39A alsoshows second sheet of material 1399, which may or may not be fashionedfrom the same sheet as sheet 1390. FIG. 39A shows the sheet afterformation of the bending strap-defining structures in the sheet butbefore sheet 1390 has been bent into its three-dimensionalconfiguration. FIG. 39B, by comparison, shows the three-dimensionalcurved channel after bending the sheet along the bend lines.

As shown in FIG. 39A, sheet 1390 includes bending strap-definingstructures 1394 (indicated only schematically because of scale) laid outto form bend curves 1393, which in this embodiment are non-linear. Indifferent embodiments, bend curves may be entirely non-linear, orcomprise linear and non-linear portions. Particular bend curves may besymmetrical or asymmetrical with other bend curves or portions ofthemselves. Bend curves may also be in the form of families of curves insheet 1390. As well, sheet periphery 1391 may in different embodimentsbe straight or curved. Many layout variations can be utilized inaccordance with the present invention.

FIG. 39B shows an embodiment of a three-dimensional curved channel 1395after bending sheet 1390 along bend curves 1393. Note that FIG. 39Bshows an embodiment formed by bending a flat sheet having a shape thatcorresponds to roughly one half of the embodiment of sheet 1390 fromFIG. 39A. In FIG. 39B, a cross section of the channel is in the shape ofa top hat and a cross-sectional area of the channel varies monotonicallyalong the length of the channel. In other embodiments, thecross-sectional area may vary in a non-monotonic manner. For example,the cross-sectional area may converge and diverge. See, for example, thesheet of FIG. 39A. A range of embodiments of curved channel 1395 issealed to be fluid-tight, as described earlier, and is therefore usefulfor fluid transport.

Depending on the material properties of sheet 1390 and the geometry ofbend curves 1393, bending or folding the sheet into a three-dimensionalstructure may cause sheet curvature out of the plane of the unfoldedsheet. Such displacement is believed to be a result of the sheetmaterial's equilibrium state being disturbed by bending. On bending, thesheet reacts to internal stresses induced by bending along the bendlines, and may deform in the process of reaching a new equilibriumstate, for example, reaching an “over-center” type state in whichbending causes the sheet to “snap” into a particular geometry. Indifferent embodiments, sheet material and bend line geometry aids orinhibits such deformation, according to design and intended use.

FIG. 39C shows an embodiment of curved channel 1395 fastened to a secondsheet of material 1399 in order to increase structural rigidity and forma hollow beam. See, in another embodiment, second sheet 1399 in FIG.39A. In a particularly straight-forward example based on the curvedchannel embodiment shown in FIG. 38B, a flat sheet is laid on top offlange 1392 (see FIG. 39B) to cover the channel; and is fastened to theflange by fastening means well-known in the art such as tack welding orscrews or rivets or bolts or pins or adhesives (not shown for clarity).The result is a hollow closed structure having enhanced bending andtorsional stiffness compared to curved channel 1395 as an openstructure.

Different embodiments combine curved channel 1395 with second sheet 1399that is not flat. The results are closed, hollow structures, many ofwhich are well-suited to be used as beams. For example, two identicalcurved channels fastened along flanges 1392 form a curved box beam. Manysuch variations can be utilized in accordance with the presentinvention.

As well, some embodiments of hollow closed structures include fillmaterial placed inside of the hollow structure to effect furtherstiffening. For example, a hollow closed structure may be filled withfoam, or a fill material comprising metal or plastic or fibrous materialand a foaming agent. These and many other variations can be utilized inaccordance with the present invention.

Turning now to other embodiments, individual structural members such asbeams or channels or “L” shaped forms made with a single fold of a sheetmay be joined by well-known means such as welding or brazing orfasteners. However, the origami-like process of precision formingthree-dimensional structures from a two-dimensional sheet, as describedin detail above, enables lightweight monocoque frameworks comprisingload-bearing members formed from a single sheet, not several sheets. Forexample, box beams, whether curved or straight, also can be used inexoskeletal designs in order to provide high strength-to-weightadvantages. Rather than using a solid beam or framework with itsattendant weight, hollow, folded or bent beams can have correspondingstrength but lower weight. If desired, such hollow beams also can befilled as described above.

FIG. 40A-FIG. 40H illustrates an example of forming an exoskeletalframework from a single sheet of material. In some aspects, theprinciples of this embodiment are similar to those exemplified by theladder structure illustrated in FIG. 32A but may result in a simplifiedstructure particularly suited for frame-like structures. FIG. 40A showsa single sheet of material prepared for folding. As a series, thesubsequent figures show the folding process that results in athree-dimensional closed framework. FIG. 40A-FIG. 40H are schematic inthat the details of bending strap-defining structures along bend linesare not shown. Different embodiments of such structures are described indetail above.

In FIG. 40A-FIG. 40H, sheet 1400, removed portions 1401, attachment tabs1402, fastener-receiving openings 1403, bend lines 1404, folded portions1405-1407, and clasps 1408 are shown. In FIG. 40A, the sheet has beenformed with bending strap-defining structures and bend lines asdescribed in detail above. Also, removed portions 1401 have been cut outto enable a final frame-like structure that is closed upon itself, butotherwise open.

FIG. 40B-FIG. 40H illustrate one embodiment of a folding sequence. InFIG. 40B, folded portions 1405 are bent along bend lines 1404(b) to forma member with an “L” cross section. Likewise, FIG. 40C-FIG. 40D showfolded portions 1406-1407 bent along bend lines 1404(c)-(d),respectively. As a result, members with “L” shaped cross sections are ontop, bottom and middle portions of sheet 1400. Continuing the sequence,the two-dimensional sheet is formed into a three-dimensional skeletalstructure by folding along bend lines 1404(e)-(h), as in FIG. 40E-FIG.40H. In each of these steps, attachment tabs 1402 extend one overanother in an interleaved manner such that fastener receiving openings1403 (see FIG. 40A) in the attachment tabs line up. Once aligned,fasteners introduced into the fastener receiving openings and clasps1408 secure this embodiment of a skeletal framework against unfolding.Many alternatives for securing such a structure are possible and can beutilized in accordance with the present invention.

According to a broad aspect of the principles described here, form mayfollow function in that the form and attendant rigidity of a foldedsingle sheet may be tailored to intended use. For example, in theembodiment shown in FIG. 40A-FIG. 40H, cross sections of the members ofthe framework are “L” shaped. In other embodiments, framework membershave differing cross sections including, but not limited to, “C” shaped,triangular-shaped and box-shaped cross sections, as well as differingattendant bending and torsional rigidities, all according to intendeduse.

FIG. 41 shows a corner portion of an embodiment of a skeletal framework,which is similar to the embodiment shown in FIG. 40A-FIG. 40H. Theembodiment in FIG. 41, however, includes members having differentbending and torsional rigidities by virtue of different cross sectiongeometry. FIG. 41 also shows a folding sequence a)-e) for the cornerportion.

FIG. 41 shows “L” shaped cross section portions 1411, channel crosssection portion 1412, bend lines 1413 and 1413(b)-(e), channel wall1415, attachment tab 1416, surface slot 1414, sheet surface 1419, andedge slot 1417. In FIG. 41, bend strap-defining structures lay along thebend lines, but are omitted for clarity and instead schematically shownas centerlines extending along the fold lines. See above for details asto bend strap-defining structures.

In FIG. 41, “L” cross section portions 1411 result from bending alongone bend line, and are like “L” cross section portions in the embodimentshown in FIG. 40. In contrast, the embodiment of FIG. 41 includeschannel cross section 1413 folded upon sheet surface 1419 by bendingalong several bend lines. The result, as shown, is a closed box beam,which has different bending and torsional rigidity than “L” crosssection portions. Including such box beams as cross members isadvantageous in supporting heavy transverse loads, for example in anequipment rack. Alternate cross section shapes, such as polygons, can beutilized in accordance with the present invention.

FIG. 41 a)-e) illustrates a folding sequence that is similar to thefolding sequence in FIGS. 40A-H. In FIG. 41 a), sheet 1419 is flat.Folding along bend lines 1413(b)-(c) according to FIG. 41 b)-c) resultsin formation of channel cross section portion 1412. In the particularembodiment shown, portions of channel wall 1415 are formed anddimensioned to include edge slots 1417, which mate as shown withcorresponding surface slots 1414. Once mated, a fastener such as, forexample, a rivet may by introduced into both slots to increase thestructure's rigidity. See FIG. 42A-FIG. 42C for more detail.

FIG. 41 c)-d) shows another aspect of securing portions of a skeletalstructure to increase the structure's rigidity. Attachment tab 1416,once bent into position along bend line 1413, couples one “L” crosssection portion 1411 to channel cross section portion 1412 with afastener such as a screw (not shown). As with attachment tabs like thoseshown in FIG. 40, this coupling contributes to tying the entire skeletalstructure together, thereby distributing loads and increasing thestructure's rigidity. As in FIG. 40, contact between attachment tabs andother portions of the structure is sheet surface to sheet surface with afastener therethrough. One will appreciate that numerous otheroverlapped sheet portions may be fastened in a like manner.

FIG. 42A-FIG. 42C show details of a corner portion of the skeletalframework embodiment in FIG. 41 b). FIG. 42A shows channel wall 1415,sheet surface 1419, bending line 1413(b), surface slot 1414, edge slot1417, edge slot walls 1420, and nubs 1421. FIG. 42B-FIG. 42C showdetails around the edge slot region for two embodiments. As in FIG. 42A,FIG. 42B-FIG. 42C show edge slot 1417, edge slot walls 1420, and nubs1421. In addition, FIG. 42B shows shoulder regions 1422 of the edge slotwalls, and FIG. 42C shows flare regions 1423 of the edge slot walls.

As described above, folding to the position shown in FIG. 41 c) fromthat shown in FIG. 41 b) and FIG. 42A involves nubs 1421 engaging andpassing through corresponding surface slots 1414. Once mated andaligned, a fastener such a rivet or a screw (not shown) may be placedinto the mated surface and edge slots to engage portions of slot walls1420 in differing manners according to different embodiments. Coupled inaccordance with the present invention in any number of manners, theresulting structure is comparatively more rigid.

FIG. 42B and FIG. 42C illustrate two examples. FIG. 42B shows anembodiment including shoulder regions 1422 of edge slot walls 1420. Theshoulder regions are located at a base portion of edge slot 1417 andprovide a land for the purpose of receiving and engaging a fastener edge(not shown), for example a rivet edge. FIG. 42C shows an alternateembodiment including flare regions 1423 of edge slot walls 1420. Theflare regions of the slot walls are located at a base portion of edgeslot 1417 and provide a flared surface to receive a fastener such as ascrew (not shown). Applying torque to the screw results in screw threadsengaging slot walls. 1420 along the length of edge slot 1417. In mostembodiments, tapping threads in the slot wall prior to fastening is notnecessary because channel wall 1415 is thin.

FIG. 40-FIG. 42C illustrate framework embodiments that include linearstructural members, however, one will appreciate that curved structuralmembers may by used. Other embodiments include a framework of curvedstructural members formed from a single sheet. In one example, FIG.43A-FIG. 43C show an embodiment with three curved channels. In otherexamples, such channels may be secured to a second sheet of material toform a hollow closed structure, as described above. Further, such hollowstructures may be filled with a stiffening filler material, which isalso described above.

FIG. 43A and FIG. 43B, respectively, show a sheet of material before andafter folding to become an exoskeletal framework of three-dimensionalcurved channels. Both figures show sheet 1430, sheet periphery 1431,flanges 1432, bend curves 1433, bending strap-defining structures 1434,channels 1435, nexus region 1436, and finger tabs 1437. FIG. 43A showsthe sheet after formation of the bending strap-defining structures inthe sheet. FIG. 43B, by comparison, shows the three-dimensional curvedchannel after bending the sheet along the bend lines. Details of thebending strap-defining structures, however, are omitted in both figuresfor clarity.

As shown in FIG. 43B, channels 1435 are curved and extend out of theoriginal plane of sheet 1430 after bending along the bend curves atleast partially due to the curvature of the bend lines. As shown, thedeformation out of the original plane is profound in this embodiment.Alternate embodiments may deform to a greater or lesser degree dependingon material properties, layouts of bend curves or pressing or formingunrelated to bending along bend curves. Also, while the embodiment inFIG. 43A-FIG. 43B has channels with converging-diverging cross sections,other embodiments have converging channels, or a combination ofconverging channels and converging-diverging channels. One willappreciate that various geometries may be used in accordance with thepresent invention.

FIG. 43C shows details of a central region of the exoskeletal frameworkin FIG. 43B. Like FIG. 43A and FIG. 43B, FIG. 43C shows sheet 1430,sheet periphery 1431, flanges 1432, bend curves 1433, bendingstrap-defining structures 1434, channels 1435, nexus region 1436, andfinger tabs 1437. In addition, FIG. 43C shows stiffening ribs 1438,finger tab opening 1439, and curved finger tab portion 1440. As before,details of the bending strap-defining structures are omitted forclarity.

In FIG. 43C, portions of sheet 1430 have been removed to form fingertabs 1437. The finger tabs enable the framework to accommodate sheetdeformation, especially deformation out of the original plane of thesheet. That is, the plane of the sheet prior to bending (see FIG. 43A).Accordingly, the finger tabs are preferably located adjacent torelatively high curvature portions of bend lines 1433. In the embodimentof FIG. 43C, the greatest deformation is proximal to nexus region 1436.Accordingly, finger tabs 1437 are proximal to the nexus region. Otherembodiments, however, may include finger tabs at different or additionallocations, depending on the desired deformation.

Nexus region 1436 takes a range of shapes in differing embodiments ofskeletal frameworks. As compared to the nexus region in FIG. 43A, otherembodiments have a more elliptical or circular nexus region. Still otherembodiments have a nexus region that is more polygonal than that of theembodiment in FIG. 43A. In yet another range of embodiments, the nexusregion is a hub-like, separable, discrete piece. With a hub-like nexusregion, the hub-like piece is formed and dimensioned to receivestructural members such as beams or channels. The structural members maybe attached to the hub as described above, or in numerous ways that arein accordance with the invention.

As described, embodiments of a skeletal framework may be highly curved.In some embodiments, any one or more than one of finger tabs 1437include curved portion 1440 at a distal end. Such a curved portion isadvantageous for some embodiments because it better accommodatessecuring to another curved piece; for example when forming a hollowclosed structure as described in detail above. With a curved portion,the distal ends of finger tabs may follow the same or similar curvatureas flange 1432 when the framework structure extends out of the originalplane of sheet 1430. See FIG. 43A-FIG. 43B. Without such a curvedportion, the distal ends of finger tabs are flat; which may or may notbe adequate for securing the finger tab to another piece, depending onthe degree of curvature of the overall skeletal framework.

In some embodiments, one or more than one of the finger tabs 1437 arestamped. Stamping may form curved portion 1440, as well turn distal endsof a finger tab out of the original plane of sheet 1430. In stamping thesheet in and around nexus (or hub) region 1436, with respect to fingertabs 1437 or otherwise, progressive dies may be utilized.

The embodiment of FIG. 43C also includes stiffening ribs 1438.Preferably, ribs are stamped into sheet 1430 with the effect ofstiffening the sheet by altering the local cross section geometry. In analternative, material may be added to the sheet to form a stiffeningrib.

In different embodiments, stiffening ribs may be located along bendlines 1433 and/or along finger tabs 1437. The embodiment in FIG. 43Cshows a stiffening rib proximate to a bend line 1433, and in substantialalignment with the bend line. In this instance, a stiffening rib isadvantageous because of the comparatively high curvature of nexus region1436. Without stiffening, the sheet may buckle.

Likewise, FIG. 43C shows stiffening ribs located proximal to and withinfinger tabs 1437. Within a finger tab, stiffening ribs are preferablyconstructed in pairs oriented such that respective longitudinal axes ofthe stiffening ribs intersect at or beyond a distal end of the fingertab. As FIG. 43C suggests, such orientation has the effect of formingminiature columns within the finger tab, which experience shows to beadvantageous for transferring stress without budding. Further, theembodiment in FIG. 43C includes an opening in between two stiffeningribs in finger tabs, which is believed to be advantageous in forming acolumn-like structure in the finger tab. Other embodiments includefinger tabs having stiffening structures such as flanges on all or aportion of the finger tab periphery. Such openings and stiffening ribswithin a finger tab, or peripheral flanges, however, are not essential.

Turning now to FIG. 44, a three-dimensional skeletal framework 1440 isillustrated which is also formed by flat sheets of material. Skeletalframework 1440 is in the form of a stand that includes a base 1441 and atop 1442. Both the base and the top are formed from flat sheets ofmaterial that has been provided with bend lines in a manner similar tothat discussed above. In some instances, it may be possible to form thetop from the same sheet of material from which the base is formed. Oncethe base and the sheet have been bent along their bend lines to formthree-dimension structures, they are assembled together to form theillustrated framework 1440. During assembly, the base and top areaffixed by suitable fasteners such as rivets, screws, nuts-and-bolts,adhesives, and/or other suitable means.

In this embodiment, the sheet material(s) are configured to allow forand to accommodate the warping of planar panels upon assembly of the topand base. For example, top 1442 is formed form a flat sheet of materialpopulated with bend lines in a manner that is discussed above.According, all portions of the top are originally planar. For example,panel 1443 is originally a planar panel prior to assembly. Duringassembly, panel 1443 develops an area of warpage 1444 once its ends areaffixed to upper ends of legs 1445 and 1445, as can be seen in FIG. 44.In particular, the panel 1443 warps such that its leftmost surfacesconform with the uppermost surfaces of leg 1445, while its rightmostsurfaces conform with the uppermost surfaces of leg 1446. As legs 1445and 1446 are skewed with respect to one another, the surface of panel1443 warps in order to accommodate the non-planar surfaces of legs 1445and 1446. With reference to FIG. 44, panel 1443 warps significantly inarea 1444, however, one will appreciate that the panel may also warp, invarying degrees outside of area 1444. On will appreciate that legs 1445and 1445 may also warp in a similar manner in varying amounts.

The configuration of framework 1440 utilizes the relatively thin-wallproperties of sheet materials to allow for warpage, and thus allow for awide variety of designs having complex geometries. While bend lines 1447are substantially linear, once base 1441 and top 1442 are bent alongtheir respective bend lines and assembled, base 1441 and top 1442include panels having complex geometries with compound-curved surfacesand edges. For example, edges 1448 and 1449 trace skew curves, that is,curves which do not lie in one plane. One will appreciate that such a“warping” configuration may be utilized for a wide variety ofthree-dimensional structures and a wide variety of geometrical shapes.

The distribution and width of bending straps may vary along the lengthof a given bend-line for a variety of reasons including a variation inthe trade-off between the local force required for bending and theresidual strength of the un-reinforced bend. For example, adjacentfeatures that may be opportunistically formed at the same time as thebending straps of the present invention may approach the bend-line soclosely that the nearest bending straps are best formed with lessfrequency near the approaching feature or with thinner straps tomaintain planarity of the bent material.

Finally, the bent structures of the present invention can be easilyunbent. This allows three-dimensional structures to be disassembled orunfabricated for transport to another site or for recycling of the sheetmaterial. It has been found that the bent sheet material can often bestraightened out, or even subject to a bend reversal, and thereafterre-bent through 5 to 10 or more cycles. This allows bending orfabrication of a structure at one site and then unbending,transportation and re-bending at a second site. The ease of unbendingalso enables structures to be unbent and sent to a recycling center forreuse of the sheet material and removed components.

For convenience in explanation and accurate definition in the appendedclaims, the terms “up” or “upper”, “down” or “lower”, “inside” and“outside” are used to describe features of the present invention withreference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the Claims appended hereto and theirequivalents.

1. A sheet of material formed for bending along a bend line, the sheetof material comprising: a plurality of slits positioned along andproximate to the bend line, each slit having slit end portions divergingaway from the bend line, each slit defining a tongue displaced laterallyout of the plane of the sheet of material prior to bending of the sheetof material.
 2. The sheet of material of claim 1, wherein the slits arepositioned on alternating sides of the bend line, and the end portionsof longitudinally adjacent slits define bending straps each having acentral axis oriented obliquely with respect to the bend line.
 3. Thesheet of material of claim 2, wherein the central axes of adjacentbending straps are skewed in alternating directions.
 4. The sheet ofmaterial of claim 2, wherein the bending straps each have a widthdimension which increases with distance on both sides of a minimum widthdimension.
 5. The sheet of material of claim 1, wherein the end portionsof the slits are arcuate end portions.
 6. The sheet of material of claim1 wherein edges of the slits engage and slide on opposing faces of thedisplaced tongues during bending.
 7. The sheet of material of claim 1,wherein: the slits are positioned on alternating sides of the bend line;the slit end portions of pairs of longitudinally adjacent slits arearcuate slit end portions defining bending straps each having a centralaxis oriented obliquely with respect to the bend line; and the centralaxes of adjacent bending straps are skewed in alternating directions. 8.The sheet of material of claim 1, wherein each slit comprises a centralportion substantially parallel to and offset laterally from the bendline.
 9. The sheet of material of claim 8, wherein the slits arepositioned on alternating sides of the bend line, and the slit endportions of longitudinally adjacent slits define bending straps eachhaving a central axis oriented obliquely with respect to the bend line.10. The sheet of material of claim 9, wherein the central axes ofadjacent bending straps are skewed in alternating directions.
 11. Thesheet of material of claim 9, wherein the bending straps each have awidth dimension which increases with distance on both sides of a minimumwidth dimension.
 12. The sheet of material of claim 8, wherein the endportions of the slits are arcuate end portions.
 13. The sheet ofmaterial of claim 8 wherein edges of the slits engage and slide onopposing faces of the displaced tongues during bending.
 14. The sheet ofmaterial of claim 8, wherein: the slits are positioned on alternatingsides of the bend line; the slit end portions of pairs of longitudinallyadjacent slits are arcuate slit end portions defining bending strapseach having a central axis oriented obliquely with respect to the bendline; and the central axes of adjacent bending straps are skewed inalternating directions.
 15. The sheet of material of claim 1, whereinthe slits are arcuate in shape.
 16. The sheet of material of claim 15,wherein the slits are positioned on alternating sides of the bend line,and the slit end portions of longitudinally adjacent slits definebending straps each having a central axis oriented obliquely withrespect to the bend line.
 17. The sheet of material of claim 15, whereinthe central axes of adjacent bending straps are skewed in alternatingdirections.
 18. The sheet of material of claim 15, wherein the slits arecontinuous arcs.
 19. The sheet of material of claim 15, wherein theslits are elongated arcuate slits.
 20. The sheet of material of claim 15wherein edges of the slits engage and slide on opposing faces of thedisplaced tongues during bending.
 21. The sheet of material of claim 15,wherein: the slits are positioned on alternating sides of the bend line;the slit end portions of longitudinally adjacent slits are arcuate slitend portions defining bending straps each having a central axis orientedobliquely with respect to the bend line; and the central axes ofadjacent bending straps are skewed in alternating directions.
 22. Thesheet of material of claim 21, wherein the slits are continuous arcs.23. The sheet of material of claim 21, wherein the slits are elongatedarcuate slits.
 24. A coil comprising the sheet of material of claim 1co-wound with a polymer web.